Java vs C# – Part 2

Introduction

This is part two of a series of posts on Java and C#. You can read the first part, on structure, here. This time, we are going to talk about a lot of things that weren’t covered before, and leave some stuff for future posts! Smile

Object and Collection Initialization

C# offers an interesting syntax for initializing instance properties at the same time a variable is declared, which can be combined with parameterized constructors:

MyClass c = new MyClass("constructor argument") { OneProperty = 1, AnotherProperty = "two" };

It also offers a syntax for defining the values of a collection upon declaration:

List<string> list = new List<string>{ "A", "B", "C" };

Dictionary<int, string> dictionary = new Dictionary<int, string>{ { 0, "A" }, { 1, "B" } };

Any class with an instance Add method can use this syntax, because it’s this method that the compiler calls behind the scene. Inside the { }, we need to pass as many elements as the Add method takes, and of the same type.

Casts

In Java, we only have one kind of cast between types:

Object o = ...;

String s = (String) o;

But in C#, we have two: the same as in Java, plus a “dynamic”, that returns null if the types are not compatible:

Object o = 1;

String s = o as String; //s is null

The as operator can only be used with reference types (classes and interfaces) and nullable types (like int ?). It does not automatically use conversion operators (see below).

In C# there’s also something related, the null coalescing operator. Basically, it allows this syntax for initializing a variable to some value only if it is null:

Object o1 = null;

Object o2 = new MyClass();

Object o3 = o1 ?? o2; //short for: o1 == null ? o3 : o1

Methods

Undefined Number of Parameters

Both Java and C# support methods with an undefined number of parameters. The syntax is slightly different, in C# being:

public void Print(params String [] args)

{

}

An in Java:

public void print(String... args)

{

}

Default Parameter Values

C# allows setting default parameter values. The default values can only be:

  • null;
  • Literals (“string”, 1, false, etc);
  • Enumerated values (MyEnum.Value);
  • Constant or read-only fields (MyClass. SomeField).
public void SayHello(String to = "me")

{

}

A method can have any number of parameters with default values, but these parameters need to come at the end, after any other parameters without default values. Java does not offer default parameter values, we have to use method overloading for that.

Changing Parameter Order

C#, unlike Java, also allows passing parameters in any order, by name, which is very useful when we have methods with a lot of parameters, and we don’t want to remember their exact order:

public void DoSomething(int a, string b)

{

}


DoSomething(b: "a string value", a: 10);

Passing Parameters by Reference

C# has two ways to pass parameters:

  • By value, the default, which is a pointer for reference types – classes and interfaces – and the actual value for value types – enumerations, structures;
  • By reference: the actual address of the variable is passed, similar to ** or & in C++.

Passing parameter values by reference can be done in one of two ways:

  • Forcing the parameter to have a value set;
  • Not forcing the parameter to have a value set.

One example that forces assignment uses the out keyword:

public void Execute(out int result)

{

    result = 0;

}

And if no assignment is required, we use ref instead:

public void Swap(ref int a, ref int b)

{

    int c = a;

    a = b;

    b = c;

}

Both out and ref are functionally equivalent, but out enforces a compile-time constraint that the parameter has a value set. Passing values by reference is particularly useful in the case of structures, because, since they are not passed by pointer, they need to be copied byte by byte, which can take some time, and they might also be boxed if the method argument is of a reference type; passing structures by reference only sends the address of the local variable.

By comparison, Java always passes parameters by value, meaning, basic types pass their actual bytes and the others are passed as pointers to the original variable.

Extension Methods

C# offers the concept of extension methods. An extension method appears to be part of some type, as an instance method of that type, but it doesn’t break encapsulation, because it really isn’t part of it, and it doesn’t have access to the type’s internals.

Extension methods are defined as static methods in static classes with a this parameter of the target type:

namespace Extensions

{

    public static class StringExtensions

    {

        public static String Revert(this String s)

        {

            //...

        }

    }

    }

We call an extension method just as we call a regular method, provided that the class that defines it is in context, either by being in the same namespace as the calling method’s class, or by having its namespace imported.

using Extensions;//this is where the StringExtensions class lives


//...


String text = "abcd";

String reverted = text.Revert();

Java has virtual extension methods, also called default methods, which provide a default implementation of a method in an interface, which is then inherited (and can be overridden) by classes implementing the interface. This is the building block for the Stream API introduced recently. I talked about default methods on the first part of this series, but here’s an example.

public interface MyInterface

{

    default void doSomething()

    {

        //do something

    }

}

Default methods are always public, so there’s no need to use the public qualifier.

Static Interface Methods

Java also allows defining static methods, with implementation, in interfaces:

public interface MyInterface

{

    static void doSomethingElse()

    {

        //does something else

    }

}

Like default methods, static interface methods are always public.

C# doesn’t have any way to add statics or code to interfaces.

Synchronized Methods

Both languages allow a method, static or instance, to be declared as synchronized, meaning, it will lock the object on which it is being called (or the class, if it is a static method). The Java syntax is:

public synchronized void myMethod()

{

    //I am synchronized

}

While the C# one use the MethodImplAttribute attribute:

[MethodImpl(MethodImplOptions.Synchronized)]

public void MyMethod()

{

    //I am synchronized

}

The syntax for acquiring a lock on an object is identical, but Java uses the synchronized keyword:

synchronized (this.someLock)

{

    //...

}

And C#, lock:

lock (this.someLock)

{

    //...

}

Inline Methods

In C#, it is possible to instruct the compiler to try to inline certain methods, through the MethodImplAttribute attribute:

public class Something

{

    [MethodImpl(MethodImplOptions.AggressiveInlining)]

    public void ShouldBeMadeInline()

    {

    }

}

The actual decision, however, is up to the compiler. Java does not allow this.

Operator Overloading

Overloadable Operators

In C#, most operators (arithmetic, comparison, bitwise) can be overloaded for a class, similarly to C++. This means that C# allows them to be redefined, so as to implement a more friendly syntax, or just change the default one:

public static bool operator == (MyClass c1, MyClass c2)

{

    return c1.MyProperty == c2.MyProperty;

}

In this example, I am changing the default == operator, which just does a reference comparison, to a value comparison, where the actual contents of the class are compared. If we change ==, we also need to change !=:

public static bool operator != (MyClass c1, MyClass c2)

{

    return !c1 == c2;

}

Some of the basic operators (+=, for example), cannot be defined explicitly, but can be defined from others (+):

public static MyClass operator + (MyClass c1, MyClass c2)

{

    return new MyClass(c1.MyProperty + c2.MyProperty);

}

It is also possible to compare unrelated classes, but the declaring class must appear as one of the arguments:

public static bool operator == (MyClass c, String s)

{

    return c.MyProperty == s;

}

The argument order defines if the operator is to be applied, for example, the previous code applies to:

MyClass c = new MyClass();

bool areEqual = c == "some string";

But not to:

MyClass c = new MyClass();

bool areEqual = "some string" == c;

We can, however, add two times the same overloadable operator with the arguments switched, so that they can be called interchangeably. The String class overrides the == operator, so as to always do comparisons by value.

The number of arguments is defined by the operator, there are unary and binary operators, and the types they return cannot be changed. For example, operator == always expects two arguments of any kind but has to return a bool.

Type Conversions

C# also features a special kind of operator: type conversion. Actually, there are two, for implicit and explicit conversions. Implicit conversions do not need an explicit cast:

public static implicit operator string (MyClass c)

{

    return c.MyProperty; //MyProperty is of type string

}


MyClass c = new MyClass();

string s = c;

Whereas explicit ones do:

public static explicit operator int (MyClass c)

{

    return int.Parse(c.Property); //MyProperty is of type string

}


MyClass c = new MyClass();

int s = (int) c;

All operators need to be public and static.

Attributes

Attributes are static metadata that can be added to types, packages, parameters, members, variables and assemblies (in C#). Some attributes have meaning to the compiler, and in C#, they can even be used as an Aspect-Oriented Programming (AOP) mechanism, because some system attributes are evaluated at runtime.

Java offers the following out of the box attributes (called annotations in Java):

  • @FunctionalInterface: declares an interface as a functional interface (an interface with a single method);
  • @Override: informs the compiler that the method to which it is applied is an override of a method with the same name and signature declared in a base class;
  • @Deprecated: marks the method as deprecated, which issues a compile-time warning;
  • @SafeVarargs: suppresses warnings related to the (mis)use of varargs (undefined number of parameters);
  • @SuppressWarnings: tells the compiler to suppress certain warnings, passed as parameters.

There are also meta-annotations, annotations that apply to other annotations:

  • @Retention: how is the annotation kept after compilation (SOURCE: only at source level, stripped at compilation, CLASS: kept at compile time, but ignored by the Java VM, RUNTIME: kept after compilation and considered by the JVM);
  • @Documented: when the annotation is applied, some elements should be documented with JavaDocs;
  • @Target: the single target of an annotation (ANNOTATION_TYPE: other annotations, CONSTRUCTOR: constructors only, FIELD: fields, LOCAL_VARIABLE: local variables inside methods, METHOD: methods, PACKAGE: packages, PARAMETER: method parameters or TYPE: any elements of classes);
  • @Inherited: the annotation can be inherited from the type’s base class;
  • @Repeatable: the annotation can be applied several times.

As you can see, an annotation starts with a @ and must be defined as an interface using a special syntax:

@Target(value=CLASS)

public @interface MyAnnotation

{

    String name() default "";

    int number();    //required since a default was not supplied

}

Annotation methods can only return basic types, enumerations and arrays of them, and cannot take parameters.

The application of the MyAnnotation annotation can be:

@MyAnnotation(number = 10) //uses default value for name

public class MyClass

{

}

In C#, attributes are not totally different, but there are some differences:

  • An attribute must inherit from the Attribute class, and, by convention, should have the Attribute suffix;
  • When applied, we can leave out the Attribute suffix;
  • Attribute’s members can only be of basic types, enumerations, or arrays of them;
  • Required attribute properties should be passed in the attribute’s constructor.

There are lots of attributes included in the .NET, so it is not practical to cover them all. I leave just some examples:

By applying an AttributeUsageAttribute, we can specify:

  • AllowMultiple: if there can be many occurrences of this attribute, in the same element;
  • Inherited: if the attribute’s presence and values is inherited in descending classes;
  • ValidOn: the elements to which the attribute can be applied (All, Assembly, Class, Constructor, Delegate, Enum, Event, Field, GenericParameter, Interface, Method, Module, Parameter, Property, ReturnValue, Struct).

Here’s an example of a C# attribute:

[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct, Inherited = true, AllowMultiple = false)]

public class MyAttribute : Attribute

{

    public MyAttribute(String required)

    {

        this.Required = required;

    }


    public String Required { get; private set; }


    public Int32 Optional { get; set; }

}

And its usage, notice that we leave out the Attribute suffix and the declaration syntax:

[My("name", Optional = 10)]

public struct MyStruct

{

    //...

}

Exceptions

Throwable Types

In .NET, any type can be thrown as an exception, but C# limits this to instances of the Exception class, or one derived from it.

In Java, we can only throw classes that implement the Throwable interface. The most common example of one such class is Exception.

Checked Exceptions

In Java, methods in classes, enumerations and interfaces must declare any exceptions that they may throw, except those inheriting from RuntimeException; these are considered special, in that they can be thrown at unforeseen situations – a division by zero, a null pointer access, etc. The syntax is for declaring the “expectable” exceptions is:

public void myMethod() throws MyException

{

}

Calling any method that declares that it may throw an exception requires that the calling code be wrapped in a try…catch block, where all checked exception types must be explicitly handled, or, of course, a superclass of them (catch is polymorphic):

try

{

    myMethod();

}

catch (MyException ex)

{

}

In both languages, more specific exception classes need to be catched first, that is, if you want to catch an Exception and a MyException that inherits from Exception, the catch block for MyException must be the first. C# allows you to omit either the class variable or even the class, if it doesn’t matter:

try

{

    //...

}

catch(MyException)

{

    //no need to refer to the exception instance

    throw;  //no argument required

}

catch

{

    //all other exception types

}

Rethrowing Exceptions

In Java as in C#, we can rethrow an exception caught in a catch clause:

try

{

    //...

}

catch (Exception ex)

{

    throw ex;

}

However, if we do it like this in C#, we lose the stack trace prior to the method issuing the throw. If we don’t want that, the alternative syntax is:

try

{

    //...

}

catch (Exception ex)

{

    throw;

}

Notice that if we don’t pass an argument to throw, it will rethrow the current exception – of course, this only works inside a catch clause.

Iterations

In C# and in Java we can iterate through the elements of a collection using either iterators or a specific syntax, which for C# is:

foreach (String item in list)

{

    //...

}

And for Java:

for (String arg : args)

{

    //...

}

In C#, any collection that has a method GetEnumerator returning an IEnumerator can benefit of this syntax, normally, all collections inheriting from IEnumerable (non-generic) or IEnumerable<T>. Java has a similar requirement, but the method needs to be called iterator and the required interface is Iterator<T>, which is implemented by most collections.

Returning Enumerables

In C#, if we want to return enumerations of values from a method, we normally prototype the method as returning IEnumerable<T>. If we do, we have a simplified syntax for returning individual values from it:

public IEnumerable<String> GetPhrases()

{

    var count = 0;


    for (var s in listOfStrings)

    {

        if (++count == 0)

        {

            yield break;    //break loop

        }


        yield return s;    //return one value, but continue loop

    }

}

Lambda Functions

Lambda functions in C# are built upon delegates and extension methods. A lambda is just syntactic sugar for calling methods – which can be defined inline, as anonymous ones -, and are most useful in collections processing:

List<MyClass> untidyCollection = ...;

List<MyClass> sortedAndFilteredCollection = untidyCollection.Where(c => c.MyProperty > 100).OrderBy(c => c.MyProperty).ToList();

In this example, Where and OrderBy are lambda functions defined over the IEnumerable<T> interface, which is implemented by List<T>. The types of the lambda variables can be omitted. This would be the same as:

class MyClassComparer : IComparer<MyClass>

{

    public Int32 Compare(MyClass c1, MyClass c2)

    {

        return c1.MyProperty.Compare(c2.MyProperty);

    }

}


List<MyClass> FilterCollection(List<MyClass> source, Int32 value)

{

    List<MyClass> target = new List<MyClass>();


    foreach (MyClass c in source)

    {

        if (c.MyProperty > value)

        {

            target.Add(c);

        }

    }


    return target;

}


List<MyClass> SortCollection(List<MyClass> source)

{

    List<MyClass> target = new List<MyClass>(source);

    target.Sort(new MyClassComparer());

    return target;

}


List<MyClass> untidyCollection = ...;

List<MyClass> sortedAndFilteredCollection = SortCollection(FilterCollection(untidyCollection));

Uuuf… see the gain?

A lambda can have several parameters:

Func<MyClass, Int32, MyClass> multiplicationTransformation = (c, multiplier) => new MyClass(c.MyProperty * multiplier);

MyClass source = ...;

MyClass target = multiplicationTransformation(source, 10);

In Java, things are very different. First, a lambda function can only be used over a functional interface, that is, an interface implementation with a single method. A method call that takes as a single parameter a class that implements this functional interface can be made a lambda function:

interface Operation

{

    default int operate(int a, int b);

}


class Calculator

{

    int doOperation(Operation op, int a, int b)

    {

        return op.operate(a, b);

    }

}


Calculator calc = new Calculator();

Operation sumOperation = (int x, int y) -> x + y;

calculator.doOperation(sumOperation, 1, 2);

Also comparison:

List<MyClass> unsortedCollection = ...;

List<MyClass> sortedCollection = Collections.sort(unsortedCollection, (MyClass c1, MyClass c2) -> c1.getMyProperty().compareTo(c2.getMyProperty()));

And finally, action listeners:

JButton button = ...;

button.addActionListener(evt -> System.out.println("Button clicked"));

Expression Trees

Related, but even more interesting than lambda expressions, are expression trees. These can be defined using the same syntax as lambda expressions:

List<MyClass> untidyCollection = ...;

IQueryable<MyClass> untidyQueryable = untidyCollection.AsQueryable();

IQueryable<MyClass> sortedAndFilteredQueryable = untidyQueryable.Where(x => x.MyProperty > 100).OrderBy(x => x.MyProperty);

But now sortedAndFilteredQueryable is an IQueryable<T>, a standard interface for wrapping expressions that return something. From it we can access the underlying Expression, the base class for all expression

Expression expression = sortedAndFilteredQueryable.Expression;


if (expression is MethodCallExpression)

{

    MethodCallExpression methodCall = expression as MethodCallExpression;

    Method method = methodCall.Method;


    foreach (Expression arg in methodCall.Arguments)

    {

        //iterate through each argument

        if (arg is ConstantExpression)

        {

            //constant

        }

        else if (arg is MemberExpression)

        {

            //property or field

        }

    }

}

This capability to analyze at runtime an expression is the basis for, for example, translating expression trees to SQL or OData calls – Entity Framework, LINQ to SQL, NHibernate, WCF Data Services, all use expression trees. Unlike lambdas, which do not retain the expression used, just the result, expression trees do not execute, but instead describe a C# expression.

Auto Closing Blocks

Both Java and C# offer an interesting construct for making sure resources are released when they are no longer needed.

In C#, these resources must implement IDisposable, and the syntax for the using block is as this:

using (IDisposable ctx = new DisposableContext())

{

    //...

}

It allows multiple disposables in the same block:

using (var disp1 = new DisposableContext())

using (var disp2 = new DisposableContext())

{

    //...

}


In Java, the required interface is AutoCloseable and the feature is called try with resources:

try (AutoCloseable disp1 = new Something())

{

    //...

}

The syntax for having several auto-closing variables is also allowed:

try (AutoCloseable disp1 = new DisposableContext(), AutoCloseable disp2 = new DisposableContext())

{

    //...

}

This basically is the same as (in both languages):

MyClass c = new MyClass();


try

{

    //...

}

finally

{

    if (c != null)

    {

        c.Dispose();    //C#

        c.close();      //Java

    }

}

Conclusion

Well, not exactly a conclusion! There will be more posts, keep dropping by and sending your feedback! Winking smile

Again, I need to thank Roberto Cortez (@radcortez) for his review of the Java parts! Thanks, man! Winking smile

Entity Framework Code First Succinctly, Second Edition

It’s now official: I will be working on a new, updated edition, of my Entity Framework Code First Succinctly, that I wrote for Syncfusion’s Succinctly series.

The first edition was about Entity Framework 5, and a lot has happened since. I would like to ask all of my blog readers that have read Entity Framework Code First Succinctly and are into Entity Framework Code First to send me your comments, corrections or suggestions for the new edition. I will be very thankful!

Hosting HTTP Resources

Introduction

How do I host thee? Let me count the ways!

You may not have realized that .NET offers a lot of alternatives when it comes to hosting an HTTP server, that is, without resorting to IIS, IIS Express or the now gone Visual Studio Web Development Server (aka, Cassini, rest in peace); by that, I either mean:

  • Opening up a TCP port and listening for HTTP requests, or a subset of them;
  • Running ASP.NET pages without a server.

In this post I am going through some of them. Some are specific to web services, but since they understand REST, I think they qualify as well as generic HTTP hosting mechanisms.

.NET HttpListener

Let’s start with HttpListener. This is included in .NET since version 2 and offers a decent server for static contents, that is, it cannot run any dynamic contents, like ASP.NET handlers, nor does it know anything about them. You merely point it to a physical folder on your file system, and it will happily serve any contents located inside it. Let’s see an example:

using (var listener = new System.Net.HttpListener())

{

    var url = "http://*:2000/";

    listener.Prefixes.Add(url);

    listener.Start();

 

    var ctx = listener.GetContext();

 

    var message = "Hello, World!";

 

    ctx.Response.StatusCode = (Int32) HttpStatusCode.OK;

    ctx.Response.ContentType = "text/plain";

    ctx.Response.ContentLength64 = message.Length;

 

    using (var writer = new StreamWriter(ctx.Response.OutputStream))

    {

        writer.Write(message);

    }

 

    Console.ReadLine();

}

This is a very basic example that just listens on port 2000, for any host name and request, and just returns Hello, World! when contacted before shutting down.

ASP.NET ApplicationHost

Complementary to HttpListener, we have a way to execute ASP.NET handlers (ASPX pages, ASHX generic handlers and ASMX web services) in a self-hosted application domain. For that, we use the ApplicationHost class to create the ASP.NET application domain, and a regular .NET class for the server implementation. An example:

public class Host : MarshalByRefObject

{

    public void ProcessPage(String page, String query, TextWriter writer)

    {

        var worker = new SimpleWorkerRequest(page, query, writer);

        HttpRuntime.ProcessRequest(worker);

    }

}

 

//strip out bin\debug, so as to find the base path where web files are located

var path = Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location).Replace(@"\bin\Debug", String.Empty);

 

//we need to copy the assembly to the base path

File.Copy(Assembly.GetExecutingAssembly().Location, Path.Combine(path, "bin", Assembly.GetExecutingAssembly().CodeBase.Split('/').Last()), true);

 

var host = System.Web.Hosting.ApplicationHost.CreateApplicationHost(typeof(Host), "/", path) as Host;

host.ProcessPage("Default.aspx", null);

Notice the File.Copy call; this is necessary because the assembly referenced by the Default.aspx page needs to be located in the same folder as the page. An alternative to this would be to add a post build-event to the Visual Studio project:

image

I leave as an exercise to the interested readers how we can combine this with HttpListener! Winking smile

OWIN WebApp

Moving on to more recent technologies, we now have OWIN. In case you’ve been living in another world and haven’t heard of OWIN, I’ll just say that it is a standard for decoupling .NET from any particular web servers, like IIS or IIS Express. It also happens to have a self-hosting implementation – which, by the way, uses HttpListener underneath.

We need to add a reference to the Microsoft.Owin.SelfHost NuGet package:

image

After that, we just register an instance of WebApp with the default parameters, add an handler, and we’re done:

class Program

{

    public static void Configuration(IAppBuilder app)

    {

        app.Use(new Func<AppFunc, AppFunc>(next => (async ctx =>

        {

            using (var writer = new StreamWriter(ctx["owin.ResponseBody"] as Stream))

            {

                await writer.WriteAsync("Hello, World!");

            }

        })));

    }

 

    static void Main(String[] args)

    {

        using (WebApp.Start<Program>("http://*:2000"))

        {

            Console.ReadLine();

        }

    }

}

Again, no fancy dynamic stuff, just plain and simple HTTP: it waits for a request and just returns Hello, World!. It is possible to run ASP.NET MVC on top of OWIN, that is the goal of project Helios, which is currently in alpha stage. Do check out the Helios NuGet package at https://www.nuget.org/packages/Microsoft.Owin.Host.IIS/1.0.0-alpha1:

image

WCF ServiceHost

Since its release, WCF offers a way for it to be self-hosted in a .NET process. The class responsible for that is ServiceHost, or one of its descendants, like WebServiceHost, more suitable for REST. I will show an example using REST, which can be easily tested using a web browser:

[ServiceContract]

public interface IRest

{

    [WebGet(ResponseFormat = WebMessageFormat.Json)]

    [OperationContract]

    String Index();

}

 

public class Rest : IRest

{

    public String Index()

    {

        return "Hello, World!";

    }

}

 

using (var host = new WebServiceHost(typeof(Rest)))

{

    var url = new Uri(@"http://localhost:2000");

    var binding = new WebHttpBinding();

 

    host.AddServiceEndpoint(typeof(IRest), binding, url);

    host.Open();

 

    Console.ReadLine();

}

This example listens for a request of /Index on port 2000 and upon receiving it, returns Hello, World! in JSON format – because we are only sending a string, it will be wrapped in . WCF REST out of the box only supports returning data in XML or JSON format, no Text or HTML, but, to be fair, that’s not what it was meant to. Should be possible to return HTML, but, honestly, it would probably mean more work than it’s worth.

Web API HttpServer

Another web services technology in the .NET stack is Web API. Web API uses a concept similar to MVC, with controllers, models and action methods, but no views. It can be self-hosted as well, using the HttpServer class. In order to use it, install the Microsoft.AspNet.WebApi.SelfHost NuGet package. You will notice that its description claims that it is legacy, and has been replaced for another based on OWIN, yet, it is fully functional, if you don’t required it to be OWIN-compliant:

image

Because of the Web API architecture, we need to implement a controller for handling requests, :

public class DummyController : ApiController

{

    [HttpGet]

    public IHttpActionResult Index()

    {

        return this.Content(HttpStatusCode.OK, "Hello, World!");

    }

}

In this example, we do not take any parameters and just return the usual response.

Here’s the infrastructure code:

var url = "http://localhost:2000";

var config = new HttpSelfHostConfiguration(url);

config.Routes.MapHttpRoute("DefaultApi", "api/{controller}/{action}");

 

using (var server = new HttpSelfHostServer(config))

{

    server.OpenAsync().Wait();

}

The DummyController is found by reflecting the current executing assembly and applying conventions; any HTTP requests for /api/Dummy/Index will land there and the outcome will be plain text.

IIS Hostable Web Core

Now, this one is tricky. IIS, from version 7, allows hosting its core engine in-process, that is, from inside another application; this is called IIS Hostable Web Core (HWC). We can supply our own Web.config and ApplicationHost.config files and specify a root folder from which IIS will serve our web resources, including any dynamic contents that IIS can serve (ASPX pages, ASHX handlers, ASMX and WCF web services, etc). Yes, I know, this contradicts my introduction, where I claimed that this post would be about hosting web resources without IIS… still, I think this is important to know, because it can be fully controlled through code.

You need to make sure HWC is installed… one option is using PowerShell’s Install-WindowsFeature cmdlet:

Or the Server Manager application:

 

Features page

 

Because HWC is controlled through an unmanaged DLL, we have to import its public API control functions and call it with .NET code. Here’s an example:

public class Host : IDisposable

{

    private static readonly String FrameworkDirectory = RuntimeEnvironment.GetRuntimeDirectory();

    private static readonly String RootWebConfigPath = Environment.ExpandEnvironmentVariables(Path.Combine(FrameworkDirectory, @"Config\Web.config"));

 

    public Host(String physicalPath, Int32 port)

    {

        this.ApplicationHostConfigurationPath = Path.Combine(Path.GetTempPath(), Path.GetTempFileName() + ".config");

        this.PhysicalPath = physicalPath;

        this.Port = port;

 

        var applicationHostConfigurationContent = File.ReadAllText("ApplicationHost.config");

        var text = String.Format(applicationHostConfigurationContent, this.PhysicalPath, this.Port);

 

        File.WriteAllText(this.ApplicationHostConfigurationPath, text);

    }

 

    ~Host()

    {

        this.Dispose(false);

    }

 

    public String ApplicationHostConfigurationPath

    {

        get;

        private set;

    }

 

    public Int32 Port

    {

        get;

        private set;

    }

 

    public String PhysicalPath

    {

        get;

        private set;

    }

 

    public void Dispose()

    {

        this.Dispose(true);

        GC.SuppressFinalize(this);

    }

 

    protected virtual void Dispose(Boolean disposing)

    {

        this.Stop();

    }

 

    public void Start()

    {

        if (IisHostableWebCoreEngine.IsActivated == false)

        {

            IisHostableWebCoreEngine.Activate(this.ApplicationHostConfigurationPath, RootWebConfigPath, Guid.NewGuid().ToString());

        }

    }

 

    public void Stop()

    {

        if (IisHostableWebCoreEngine.IsActivated == true)

        {

            IisHostableWebCoreEngine.Shutdown(false);

 

            this.PhysicalPath = String.Empty;

            this.Port = 0;

 

            File.Delete(this.ApplicationHostConfigurationPath);

 

            this.ApplicationHostConfigurationPath = String.Empty;

        }

    }

 

    private static class IisHostableWebCoreEngine

    {

        private delegate Int32 FnWebCoreActivate([In, MarshalAs(UnmanagedType.LPWStr)] String appHostConfig, [In, MarshalAs(UnmanagedType.LPWStr)] String rootWebConfig, [In, MarshalAs(UnmanagedType.LPWStr)] String instanceName);

        private delegate Int32 FnWebCoreShutdown(Boolean immediate);

 

        private const String HostableWebCorePath = @"%WinDir%\System32\InetSrv\HWebCore.dll";

        private static readonly IntPtr HostableWebCoreLibrary = LoadLibrary(Environment.ExpandEnvironmentVariables(HostableWebCorePath));

 

        private static readonly IntPtr WebCoreActivateAddress = GetProcAddress(HostableWebCoreLibrary, "WebCoreActivate");

        private static readonly FnWebCoreActivate WebCoreActivate = Marshal.GetDelegateForFunctionPointer(WebCoreActivateAddress, typeof(FnWebCoreActivate)) as FnWebCoreActivate;

 

        private static readonly IntPtr WebCoreShutdownAddress = GetProcAddress(HostableWebCoreLibrary, "WebCoreShutdown");

        private static readonly FnWebCoreShutdown WebCoreShutdown = Marshal.GetDelegateForFunctionPointer(WebCoreShutdownAddress, typeof(FnWebCoreShutdown)) as FnWebCoreShutdown;

 

        internal static Boolean IsActivated

        {

            get;

            private set;

        }

 

        internal static void Activate(String appHostConfig, String rootWebConfig, String instanceName)

        {

            var result = WebCoreActivate(appHostConfig, rootWebConfig, instanceName);

 

            if (result != 0)

            {

                Marshal.ThrowExceptionForHR(result);

            }

 

            IsActivated = true;

        }

 

        internal static void Shutdown(Boolean immediate)

        {

            if (IsActivated == true)

            {

                WebCoreShutdown(immediate);

                IsActivated = false;

            }

        }

 

        [DllImport("Kernel32.dll")]

        private static extern IntPtr LoadLibrary(String dllname);

 

        [DllImport("Kernel32.dll")]

        private static extern IntPtr GetProcAddress(IntPtr hModule, String procname);

    }

}

In order for this to work, we need to have an ApplicationHost.config file, a minimum working example being:

<?xml version="1.0" encoding="UTF-8" ?>

<configuration>

    <configSections>

        <sectionGroup name="system.applicationHost">

            <section name="applicationPools" />

            <section name="sites" />

        </sectionGroup>

 

        <sectionGroup name="system.webServer">

            <section name="globalModules" />

            <section name="modules" />

            <section name="handlers" />

            <section name="staticContent" />

            <section name="serverRuntime" />

            <sectionGroup name="security">

                <section name="access"/>

                <sectionGroup name="authentication">

                    <section name="anonymousAuthentication" />

                    <section name="windowsAuthentication" />

                    <section name="basicAuthentication" />

                </sectionGroup>

                <section name="authorization" />

                <section name="requestFiltering" />

                <section name="applicationDependencies" />

                <section name="ipSecurity" />

            </sectionGroup>

            <section name="asp" />

            <section name="caching" />

            <section name="cgi" />

            <section name="defaultDocument" />

            <section name="directoryBrowse" />

            <section name="httpErrors" />

            <section name="httpLogging" />

            <section name="httpProtocol" />

            <section name="httpRedirect" />

            <section name="httpTracing" />

            <section name="isapiFilters" allowDefinition="MachineToApplication" />

            <section name="odbcLogging" />

        </sectionGroup>

    </configSections>

 

    <system.applicationHost>

        <applicationPools>

            <add name="AppPool" managedPipelineMode="Integrated" managedRuntimeVersion="v4.0" autoStart="true" />

        </applicationPools>

 

        <sites>

            <site name="MySite" id="1">

                <bindings>

                    <binding protocol="http" bindingInformation="*:{1}:localhost" />

                </bindings>

                <application path="/" applicationPool="AppPool" >

                    <virtualDirectory path="/" physicalPath="{0}" />

                </application>

            </site>

        </sites>

    </system.applicationHost>

 

    <system.webServer>

        <globalModules>

            <add name="StaticFileModule" image="%windir%\System32\inetsrv\static.dll" />

            <add name="AnonymousAuthenticationModule" image="%windir%\System32\inetsrv\authanon.dll" />

            <add name="ManagedEngine" image="%windir%\Microsoft.NET\Framework\v4.0.30319\webengine4.dll" />

        </globalModules>

 

        <modules>

            <add name="StaticFileModule" />

            <add name="AnonymousAuthenticationModule" />

            <add name="DefaultAuthentication" type="System.Web.Security.DefaultAuthenticationModule" preCondition="managedHandler" />

            <add name="UrlAuthorization" type="System.Web.Security.UrlAuthorizationModule" preCondition="managedHandler" />

            <add name="FileAuthorization" type="System.Web.Security.FileAuthorizationModule" preCondition="managedHandler" />

            <add name="AnonymousIdentification" type="System.Web.Security.AnonymousIdentificationModule" preCondition="managedHandler" />

        </modules>

 

        <handlers accessPolicy="Read, Script">

            <add name="PageHandlerFactory-Integrated" path="*.aspx" verb="GET,HEAD,POST,DEBUG" type="System.Web.UI.PageHandlerFactory" preCondition="integratedMode" />

            <add name="StaticFile" path="*" verb="*" modules="StaticFileModule" resourceType="Either" requireAccess="Read" />

        </handlers>

 

        <staticContent>

            <mimeMap fileExtension=".html" mimeType="text/html" />

            <mimeMap fileExtension=".jpg" mimeType="image/jpeg" />

            <mimeMap fileExtension=".gif" mimeType="image/gif" />

            <mimeMap fileExtension=".png" mimeType="image/png" />

        </staticContent>

    </system.webServer>

</configuration>

And all we need to start hosting pages on the port and physical path specified by ApplicationHost.config is:

using (var host = new Host(path, port))

{

    host.Start();

 

    Console.ReadLine();

}

A couple of notes:

  • Because it calls unmanaged functions, can be terrible to debug;
  • The ApplicationHost.config needs to be in the application’s binary build directory and must have two placeholders, {0} and {1}, for the physical path and HTTP port, respectively;
  • It refers to .NET 4.0, if you want to change it, you will to change a number of modules and paths;
  • Only very few modules are loaded, if you want, get a full file from %HOMEPATH%\Documents\IISExpress\config\ApplicationHost.config and adapt it to your likings.

.NET TcpListener

And finally, one for the low-level guys. The TcpListener class allows the opening of TCP/IP ports and the handling of requests coming through them. It doesn’t know anything about the HTTP protocol, of course, so, if we want to leverage it, we need to implement it ourselves. Here’s a very, very, basic example:

var listener = System.Net.Sockets.TcpListener.Create(2000);

listener.Start();

 

using (var client = listener.AcceptTcpClient())

{

    using (var reader = new StreamReader(client.GetStream()))

    using (var writer = new StreamWriter(client.GetStream()))

    {

        var request = reader.ReadLine();

 

        writer.WriteLine("HTTP/1.1 200 OK");

        writer.WriteLine("Content-type: text/plain");

        writer.WriteLine();

        writer.WriteLine("Hello, World!");

        writer.Flush();

    }

}

 

listener.Stop();

Here we’re just reading any string content and responding with some HTTP headers plus the usual response. Of course, HTTP is quite complex, so I wouldn’t recommend you try to implement it yourself.

Conclusion

I presented a couple of solutions for hosting web resources, servicing HTTP requests or running ASP.NET handlers. Hopefully you will find one that matches your needs.

Entity Framework Extensibility Index

Updated on March 10th.

Here you will find a list of all my posts on Entity Framework extensibility.

Freetext Extension in Entity Framework Code First

I posted before a solution for adding custom SQL functions to Entity Framework Code First as extension methods. This time I am going to show how we can do something similar for the FREETEXT function of SQL Server. Please note that this example will only work if you have the Fulltext Search component installed and your table is indexed.

OK, so we want to have an extension method like this:

[DbFunction("CodeFirstDatabaseSchema", "FREETEXT")]

public static Boolean Freetext(this String column, String value)

{

    return column.Contains(value);

}

In order for Entity Framework to recognize it, we need to write our own convention, this is because Entity Framework only recognizes out of the box a number of SQL Server built-in functions. We can write one as this:

public class FreetextConvention : IStoreModelConvention<EdmModel>

{

    public static readonly FreetextConvention Instance = new FreetextConvention();


    public void Apply(EdmModel item, DbModel model)

    {

        var valueParameter = FunctionParameter.Create("column", this.GetStorePrimitiveType(model, PrimitiveTypeKind.String), ParameterMode.In);

        var formatParameter = FunctionParameter.Create("value", this.GetStorePrimitiveType(model, PrimitiveTypeKind.String), ParameterMode.In);

        var returnValue = FunctionParameter.Create("result", this.GetStorePrimitiveType(model, PrimitiveTypeKind.Boolean), ParameterMode.ReturnValue);


        var function = this.CreateAndAddFunction(item, "FREETEXT", new[] { valueParameter, formatParameter }, new[] { returnValue });

    }


    protected EdmFunction CreateAndAddFunction(EdmModel item, String name, IList<FunctionParameter> parameters, IList<FunctionParameter> returnValues)

    {

        var payload = new EdmFunctionPayload { StoreFunctionName = name, Parameters = parameters, ReturnParameters = returnValues, Schema = this.GetDefaultSchema(item), IsBuiltIn = true };

        var function = EdmFunction.Create(name, this.GetDefaultNamespace(item), item.DataSpace, payload, null);


        item.AddItem(function);


        return (function);

    }


    protected EdmType GetStorePrimitiveType(DbModel model, PrimitiveTypeKind typeKind)

    {

        return (model.ProviderManifest.GetStoreType(TypeUsage.CreateDefaultTypeUsage(PrimitiveType.GetEdmPrimitiveType(typeKind))).EdmType);

    }


    protected String GetDefaultNamespace(EdmModel layerModel)

    {

        return (layerModel.GlobalItems.OfType<EdmType>().Select(t => t.NamespaceName).Distinct().Single());

    }


    protected String GetDefaultSchema(EdmModel layerModel)

    {

        return (layerModel.Container.EntitySets.Select(s => s.Schema).Distinct().SingleOrDefault());

    }

}

This registers a FREETEXT function with two string parameters and returning a boolean. All is fine, we add it to the DbContext in OnModelCreating:

modelBuilder.Conventions.Add(FreetextConvention.Instance);

You might have noticed the usage of a Instance static field, this is because, since the FreetextConvention class is stateless, there’s no point in creating many of them, we can just use the same instance.

Now, if we issue a LINQ query as:

var customers = ctx.Customers.Where(x => x.Name.Freetext("ricardo")).ToList();

It will fail miserably, complaining about this SQL fragment:

WHERE ((FREETEXT(name, N'ricardo') = 1)

The “= 1” part is here because the function is prototyped as boolean, which maps to SQL Server’s BIT data type, and the value for true is 1. Apparently, SQL Server does not support comparisons of some functions with 1; but if we run it as:

WHERE ((FREETEXT(name, N'ricardo'))

without the explicit comparison, it works perfectly. So, all we have to do is get rid of “= 1”. Fortunately, Entity Framework, as of version 6, offers some very nice extensibility points. There are at least two ways by which we can achieve this:

  • By intercepting the command tree;
  • By intercepting the raw SQL.

Here we will use option #2 and leave command trees for another post.

We need to identity something with a format of “FREETEXT(something) = 1”. We can do it using a regular expression, and the interception of the SQL command can be achieved by implementing IDbCommandInterceptor (no reference documentation yet, but I have reported it and it will soon be fixed, hopefully) and registering one such instance in the DbInterception (same) static class. An IDbCommandInterceptor implementation might look like this:

public class FreetextInterceptor : IDbCommandInterceptor

{

    public static readonly FreetextInterceptor Instance = new FreetextInterceptor();


    private static readonly Regex FreetextRegex = new Regex(@"FREETEXT\(([^)]+\))\) = 1");


    public void NonQueryExecuted(DbCommand command, DbCommandInterceptionContext<Int32> interceptionContext)

    {

    }


    public void NonQueryExecuting(DbCommand command, DbCommandInterceptionContext<Int32> interceptionContext)

    {

    }


    public void ReaderExecuted(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)

    {

    }


    public void ReaderExecuting(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)

    {

        var matches = FreetextRegex.Matches(command.CommandText);


        if (matches.Count > 0)

        {

            command.CommandText = FreetextRegex.Replace(command.CommandText, "FREETEXT($1)");

        }

    }


    public void ScalarExecuted(DbCommand command, DbCommandInterceptionContext<Object> interceptionContext)

    {

    }


    public void ScalarExecuting(DbCommand command, DbCommandInterceptionContext<Object> interceptionContext)

    {

    }

}

You can see that the only method we’re interested in is ReaderExecuting (again, no documentation available), with is the one that will be called just before a SQL SELECT query is sent to the database. In here we analyze the CommandText property of the DbCommand and get rid of the “= 1” clause, using a regular expression. Finally, we need to register the interceptor before we issue the query, maybe in the static constructor of our DbContext:

DbInterception.Add(FreetextInterceptor.Instance);

And now we can finally execute our query:

var customers = ctx.Customers.Where(x => x.Name.Freetext("ricardo")).ToList();

And that’s it. Don’t forget that in order for this to work, you need to enable Full Text Search.

ASP.NET Web Forms Extensibility: Control Builder Interceptors

After my previous post on Control Builders, what could possibly come next? Of course, Control Builder Interceptors! Not much documentation on this one, which is a shame, because it is an even more powerful feature that was recently introduced in ASP.NET 4.5.

A Control Builder Interceptor inherits from, unsurprisingly, ControlBuilderInterceptor. This is configured for the whole application, in the Web.config file, in the compilation section, by a controlBuilderInterceptorType (sorry, no link, since the ASP.NET 4.5 documentation is not online) attribute:

<compilation targetFramework="4.5" controlBuilderInterceptorType="MyNamespace.MyControlBuilderInterceptor, MyAssembly" />

Similarly to Control Builders, a Control Builder Interceptor allows us to:

Granted, less than Control Builders, but the point here is that this is fired for all markup-declared controls, not just those that have a specific Control Builder applied to. With that in mind, we can write code like this:

public class MyControlBuilderInterceptor : ControlBuilderInterceptor

{

    //raised for every control on markup

    public static event Action<ControlInterceptedEventArgs> ControlIntercepted;

 

    public override void OnProcessGeneratedCode(ControlBuilder controlBuilder, CodeCompileUnit codeCompileUnit, CodeTypeDeclaration baseType, CodeTypeDeclaration derivedType, CodeMemberMethod buildMethod, CodeMemberMethod dataBindingMethod, IDictionary additionalState)

    {

        var controlDeclaration = buildMethod.Statements[0] as CodeVariableDeclarationStatement;

 

        if (controlDeclaration != null)

        {

            var controlName = controlDeclaration.Name;

 

            buildMethod.Statements.Insert(buildMethod.Statements.Count - 1, new CodeSnippetStatement(String.Concat(this.GetType().FullName, ".Intercept(@", controlName, ");")));

        }

 

        base.OnProcessGeneratedCode(controlBuilder, codeCompileUnit, baseType, derivedType, buildMethod, dataBindingMethod, additionalState);

    }

 

    public override void PreControlBuilderInit(ControlBuilder controlBuilder, TemplateParser parser, ControlBuilder parentBuilder, Type type, String tagName, String id, IDictionary attributes, IDictionary additionalState)

    {

        if ((attributes != null) && (attributes.Contains("Text") == true))

        {

            //make property value uppercase

            attributes["Text"] = (attributes["Text"] as String).ToUpper();

        }

 

        base.PreControlBuilderInit(controlBuilder, parser, parentBuilder, type, tagName, id, attributes, additionalState);

    }

 

    public static void Intercept(Control instance)

    {

        var handler = ControlIntercepted;

 

        if (handler != null)

        {

            handler(new ControlInterceptedEventArgs(instance));

        }

    }

}

And there you have it. By adding an event handler to MyControlBuilderInterceptor.ControlIntercepted, we can analyze and change the properties of every control:

[Serializable]

public sealed class ControlInterceptedEventArgs : EventArgs

{

    public ControlInterceptedEventArgs(Control control)

    {

        this.Control = control;

    }

 

    public Control Control { get; private set; }

}

 

MyControlBuilderInterceptor.ControlIntercepted += e =>

{

    var myControl = e.Control as MyControl;

    

    if (myControl != null)

    {

        myControl.Text = myControl.Text.ToUpper();

    }

};

Stay tuned for more extensibility points of your favorite framework!

ASP.NET Web Forms Extensibility: Control Builders

One of the most often ignored extensibility point in Web Forms is the Control Builder. Control Builders are subclasses of ControlBuilder (or other more specialized, such as FileLevelPageControlBuilder, for pages, or FileLevelMasterPageControlBuilder, for master pages) that can be specified per class. It controls some aspects of a control instance:

It also allows overriding a couple of things:

  • The parameters specified in the markup (Init);
  • What to do when the control builder is added to a parent control builder (OnAppendToParentBuilder);
  • Modify the code that will be generated in the code-behind class that is produced by ASP.NET or the code that will be used to instantiate the control (ProcessGeneratedCode);
  • Change the tag’s inner textual content (SetTagInnerText);
  • Etc.

This is a powerful mechanism, which has even been used to allow generic control classes. We apply a control builder through a ControlBuilderAttribute (for regular controls) or FileLevelControlBuilderAttribute for pages, master pages or user controls.

I won’t go into many details, but instead I will focus on the Init and ProcessGeneratedCode methods.

Init let’s us do things such as:

public override void Init(TemplateParser parser, ControlBuilder parentBuilder, Type type, String tagName, String id, IDictionary attribs)

{

    if (type == typeof(SomeBaseControl)

    {

        //replace the control's type for another one

        type = typeof(SomeDerivedControl);

 

        //convert an hypothetical Text property value to upper case

        attribs["Text"] = (attribs["Text"] as String).ToUpper();

    }

 

    base.Init(parser, parentBuilder, type, tagName, id, attribs);

}

And ProcessGeneratedCode, messing with the generated page class:

public override void ProcessGeneratedCode(CodeCompileUnit codeCompileUnit, CodeTypeDeclaration baseType, CodeTypeDeclaration derivedType, CodeMemberMethod buildMethod, CodeMemberMethod dataBindingMethod)

{

    //add some interface to the generated page class

    derivedType.BaseTypes.Add(typeof(ISomeInterface));

 

    //add a property implementation to the generated page class

    var prop = new CodeMemberProperty();

    prop.Attributes = MemberAttributes.Public;

    prop.Name = "SomeProperty";

    prop.Type = new CodeTypeReference(typeof(String));    

    prop.GetStatements.Add(new CodeMethodReturnStatement(new CodePrimitiveExpression("Hello, World, from a generated property!")));

    

    derivedType.Members.Add(prop);

 

    base.ProcessGeneratedCode(codeCompileUnit, baseType, derivedType, buildMethod, dataBindingMethod);

}

But also something MUCH more fun! Imagine you are using an IoC container – I will use Unity, but you can use whatever you want. We might have something like this in Application_Start (or whatever method spawned from it);

var unity = new UnityContainer();

unity.RegisterInstance<MyControl>(new MyControl { Text = "Bla bla" });

ServiceLocator.SetLocatorProvider(() => new UnityServiceLocator(unity));

Notice I am using the Common Service Locator to abstract the IoC container and to make the code independent of it. Here, I am assigning a static instance to the MyControl type, in essence, a singleton.

Now, we can change our control builder so as to have the control build method return this instance:

public override void ProcessGeneratedCode(CodeCompileUnit codeCompileUnit, CodeTypeDeclaration baseType, CodeTypeDeclaration derivedType, CodeMemberMethod buildMethod, CodeMemberMethod dataBindingMethod)

{

    //return ServiceLocator.Current.GetInstance(typeof(MyControl));

    var type = Type.GetType((buildMethod.Statements[0] as CodeVariableDeclarationStatement).Type.BaseType);

    var currentProperty = new CodePropertyReferenceExpression(new CodeTypeReferenceExpression(typeof (ServiceLocator)), "Current");

    var getInstance = new CodeMethodInvokeExpression(currentProperty, "GetInstance", new CodeTypeOfExpression(type));

    var @cast = new CodeCastExpression(type, getInstance);

    var @return = new CodeMethodReturnStatement(@cast);

 

    buildMethod.Statements.Clear();

    buildMethod.Statements.Add(@return);

 

    base.ProcessGeneratedCode(codeCompileUnit, baseType, derivedType, buildMethod, dataBindingMethod);

}

In case you didn’t notice, what this does is, every time the MyControl control is instantiated in a page, for every request, ASP.NET will always return the same instance!

Now, I am not saying that you SHOULD do this, but only that you CAN do this! Winking smile

Take care out there…

Java vs C# – Part 1

Disclaimer: long post!

Introduction

While some of my friends and colleagues seem to think that I don’t like Java and that I am some sort of Microsoft/.NET zealot, that is actually not true! Smile with tongue out I do like Java, and I worked with it several years.

There are several articles out there on the differences and similarities between C# and Java, but none actually satisfied me. In this new series of posts, I will try to explain these similarities and differences, as extensively and accurately as I can. I don’t want to start a religious war, but I won’t refrain from emitting judgments on what I think is best in each. I will try to cover as much as I can, but I won’t drill into APIs, instead will focus on each language’s intrinsic characteristics.

This first post will focus on high-level constructs, what I call structure: namespaces and types. I will be covering Java 8 and C# 5, the latest (as of February 2015) versions of these languages.

Update: See the second post here.

Similarities

Both languages (Java and C#) are case-sensitive, strictly object oriented, offering classes, enumerations and interfaces, single inheritance model and all of the types live in namespaces/packages. Also, all support attributes/annotations, methods and fields, including static ones. The base class for all types, in both cases, is called Object. Both have the same basic operators, comparable base types and exception handling mechanisms. Both start executing by a static method called main/Main.

Compiled Units

A Java class compiles to an identically-named class file; these files exist on their own, but are usually stored together inside a jar, war or ear, which are basically ZIP files with a manifest file attached to, for better manageability. These files, of course, can contain other resources, such as images or text files.

C# classes always exist in binary assemblies, which can have two basic forms (extensions):

  • dll: a library, does not run on its own;
  • exe: a stand-alone executable, which can either be a Console or a Windows Forms / Windows Presentation Foundation graphical application.

Assemblies can also include metadata and embedded resources, of any type. C#/.NET actually defines another compilation unit, the module, but typically a module matches an assembly, although it is possible to have it other way, for more advanced scenarios.

Namespaces

Both in Java and in C# we have the notion of namespaces or packages, which can be nested. In C#, the namespace declaration must wrap all of its types, and therefore we can have several namespace declarations in a source file, even nested:

namespace MyNamespace1

{

    public class Class1

    {

    }

}


namespace MyNamespace2

{

    public class Class2

    {

    }


    namespace MyNamespace3

    {

        public class Class3

        {

        }

    }

}

In Java, the package declaration goes on the top of a source file, meaning, it can only contain a single package:

package myPackage;


public class MyClass

{

}

There is one important difference between Java and C#: in Java, the namespace must be identical to the physical folder structure, that is, a class belonging to the a.b package must be physically located in an a\b folder; Java won’t compile it otherwise. The generated .class file must be located in the same folder, such as a\b\MyClass.class.

Java and C# can simplify accessing classes in other namespaces/packages by importing these, like we see here for Java, where we can import all types (*), or a type at a time:

//import java.lang.*;    automatically imported

import java.io.*;

import java.lang.reflect.Array;

Java imports automatically the types in the java.lang package, C# does not automatically import any namespace, and it doesn’t allow importing a single type:

using System;

using System.IO;

But it also lets us define type aliases per source file using the same syntax:

using date = System.DateTime;


public class MyClass

{

    public date GetCurrentDate()

    {

        //...

    }

}

Top Level Elements (Types)

Java and C# offer a very close syntax, in some cases, if we discount the different language conventions, it’s really hard to tell one from the other, but there are some important differences.

Java offers the following top level elements, besides packages:

  • Classes (including generic);
  • Interfaces (including generic);
  • Enumerations.

And C# the same plus some more:

  • Classes (including generic);
  • Interfaces (including generic);
  • Enumerations;
  • Structures;
  • Delegates (including generic).

Basic Types

The basic types in the two languages (C#/Java) are:

  • Object/Object (C# shorthand: object);
  • String/String (C# shorthand: string);
  • Byte/byte (C# shorthand: byte);
  • SByte/N/A (C# shorthand: sbyte);
  • Boolean/boolean (C# shorthand: bool);
  • Char/char (C# shorthand: char);
  • Int16/short (C# shorthand: short);
  • UInt16/N/A (C# shorthand: uint);
  • Int32/int (C# shorthand: int);
  • UInt32/N/A (C# shorthand: uint);
  • Int64/long (C# shorthand: long);
  • UInt64/N/A (C# shorthand: ulong);
  • Single/float (C# shorthand: float);
  • Double/double (C# shorthand: double);
  • Decimal/N/A (C# shorthand: decimal);
  • dynamic/N/A;
  • Arrays.

As you can see, C# offers unsigned and signed versions of all integer types and also a high-precision Decimal type. It also as a dynamic type, used for late-binding (runtime) operations without strong compile-time checks.

C# offers three kinds of arrays:

  • Single dimension: int [] numbers;
  • Multi dimension: int [,] matrix;
  • Arrays of arrays, also called, jagged arrays: int [][] matrix;

Java also has single dimension and jagged arrays, but no multi dimension ones.

C# lets us use the var keyword for declaring a variable and automatically initializing it. This is a shorthand for the initialization’s type:

var i = 10;            //int

var s = "string";      //string

var f = SomeMethod();  //method's return type, except void

In C# as in Java, we can specify suffixes for clarifying the desired type of a literal:

  • 10n: integer;
  • 10l: long;
  • 10f: float;
  • 10d: double;
  • 10u: unsigned int (C# only);
  • 10ul: unsigned long (C# only);
  • 10m: decimal (C# only).

Both lowercase or uppercase letters are allowed as the suffix.

Classes

Classes in Java and C# are allocated in the heap. A class can inherit from a single base class, if not specified, it will inherit from Object. It can implement any number of interfaces.

Structures

C# has a unified type system, meaning, primitive types (integers, floating points, booleans, etc) coexist in the same type hierarchy as composite classes. This is different in Java, where, for example, the int and Integer types are not related, even if it is possible to convert between the two. All primitive types in C# are structures, not classes, which means they are allocated in the stack instead of the heap. In Java this also occurs for primitive types, but there is no notion of explicit structures, and we can’t build our own types to be stored in the stack. A structure in C# cannot inherit from any class explicitly, but it can implement any number of interfaces, and also cannot declare a destructor/finalizer:

public struct MyStructure : IMyInterface

{

    public void MyMethod()

    {

    }

}

Structures and enumerations in C# are called value types and classes and interfaces are called reference types. Because of C#’s unified type system, a structure always implicitly inherits from System.ValueType.

Interfaces

In C#, an interface can only have:

  • Instance method declarations;
  • Instance property declarations;
  • Instance event declarations.

It can be generic or non-generic. Both classes and structures can implement interfaces. An interface can always be assigned null, it is a reference type. Also, a generic interface in C# can be made covariant or contravariant.

In Java, things are a bit different, since they can have also have statics and (the horror!), method implementations:

  • Instance method declarations;
  • Fields (always implicitly static) with a value (constants);
  • Default methods: methods with default implementations.

They can also be generic or otherwise, and can be implemented by enumerations. In Java, an interface’s members can also have visibility levels defined, that is, they are not always public.

If a Java interface only has one method, or, at least, one non-default method (more on this later), it can be marked as a functional interface, in which case, it can be used in lambda functions, the method is implicitly called (see an example below in the Delegates section).

Generic Types

Generics are quite different, internally, in Java and C#. Both languages support generic classes and interfaces, but in C# they are a first-class construct, with reflection support, but in Java they cease to exist once a generic class is compiled. That is, in Java, a List<String>, at runtime, becomes just List, the generic parameter String is erased, this is in order to ensure backward compatibility with prior Java versions that didn’t have generics. This doesn’t happen in C#, and we can at runtime reflect on a generic class and its parameters.

Both languages support any number of generic parameters and constraints on them. In C# these constraints are:

  • Base class, structure or interface: forces the generic parameter to inherit or implement from a specific class, structure or interface;
  • Public non-abstract class with a public parameterless constructor: only allows generic parameters that are non-abstract (or interfaces) and have a public constructor that doesn’t take parameters;
  • Reference or value type: a generic parameter either has to be a reference (class or interface) or a value type (structure or enumeration), as specified.

An example:

public class GenericClassWithReferenceParameter<T> where T : class

{

}


public class GenericClassWithValueParameter<T> where T : struct

{

}


public class GenericClassWithMyClassParameter<T> where T : MyClass

{

}


public class GenericClassWithPublicParameterlessParameter<T> where T : new()

{

}


public class GenericClassWithRelatedParameters<K, V> where K : V

{

}


public class GenericClassWithManyConstraints<T> where T : IDisposable where T : new() where T : class

{

}

Java accepts the following constraints:

  • Base class: a generic parameter must inherit from a base class;
  • Implementing interface: a generic parameter must implement some interface;
  • Unbounded generic type: a generic parameter must inherit/implement some generic type.

Some examples:

public class GenericClassWithBaseClassParameter<T extends BaseClass>

{

}


public class GenericClassWithInterfaceParameter<T extends Interface>

{

}


public class GenericClassWithBaseMatchingParameter<T, ? super T>

{

}


public class GenericClassWithManyInterfaceParameters<T implements BaseInterface1 & BaseInterface2>

{

}


In Java, we can specify a generic of an unknown type:

MyInterface<?> var;

Java also has some terrible limitations:

  • There cannot be generics of primitive types, for example, MyGenericClass<int>, only of non-primitives, like MyGenericClass<Integer>;
  • There cannot be generic arrays.

Because C# supports any kinds of generic parameters, if we want to initialize explicitly some variable of a generic parameter type, we need to use the default keyword:

public class MyGenericClass<T>

{

    public void MyMethod()

    {

        T someField = default(T);

    }

}

Finally, the base class of some class inheriting from a generic type is not that generic type, but its base class, which can seem awkward. This happens in C# and in Java.

Delegates

A delegate in C# is a method signature, composed of:

  • A name;
  • A return type;
  • Parameters (number and type).

Delegates are the building blocks of events. A delegate can either point to a static, an instance or an anonymous method (lambda), provided the signature is the same:

public delegate double Operation(double v1, double v2);


//a delegate pointing to a static method

Operation addition = Operations.Add;


//a delegate pointing to an instance method

Operation subtraction = this.Subtract


//a delegate pointing to an anonymous method using lambdas

Operation subtraction = (a, b) =>

{

    return a + b;

};

A delegate can be generic:

public delegate void Action<T>(T item);

Delegates inherit automatically from System.Delegate, because of this, they have built-in support for dynamic and asynchronous invocation.

Java has a similar construct, functional interfaces. These are interfaces with a single non-default method, which can be used in lambda functions:

public interface MyWorkerFunction

{

    @FunctionalInterface

    public void doSomeWork();

}


public void startThread(MyWorkerFunction fun)

{

    fun.doSomeWork();

}


public void someMethod()

{

    startThread(() -> System.out.println("Running..."));

}

If an interface is marked as functional but has more than one method, it will not compile.

Enumerations

Enumerations in Java can have members (constructors, fields and methods) and even implement interfaces, something that is not possible in C#:

public enum MyEnumeration implements MyInterface

{

    A_VALUE(1),

    ANOTHER_VALUE(2);


    private int value;


    private MyEnumeration(int value)

    {

        this.value = value;

    }


    public static String fromInt(int value)

    {

        if (value == A_VALUE.value) return ("A_VALUE");

        else return ("ANOTHER_VALUE");

    }

}

In C#, no methods or interfaces, but we can have an enumeration be implemented based on a primitive integer type, including unsigned (the default is signed int):

public enum MyEnumeration : uint

{

    AValue = 1,

    AnotherValue = 2

}

Implicitly, all C# enumerations inherit from System.Enum.

In both cases, C# and Java, we can specify integral values for each enumeration member, and, if we don’t, members will get sequential values.

Type Visibilities

A type in Java has four possible visibilities:

  • package: only accessible by other classes in the same package (the default);
  • public: accessible by everyone.

And C# types have similar ones, plus one:

  • internal: only accessible by other classes in the same assembly (the default);
  • public: accessible by everyone.

Inheritance

In C#, the syntax for extending a class and for implementing an interface is exactly the same:

public class MyClass : BaseClass, IInterface

{

}

Whereas in Java there are the extends and the implements keywords, respectively, for classes and interfaces:

public class MyClass extends BaseClass implements Interface

{

}


public interface DerivedInterface extends BaseInterface1, BaseInterface2

{

}

Both can inherit from a single class and implement as many interfaces as desired. Also, an interface can itself inherit from several interfaces.

In C# it is possible to implement interfaces in one of two ways:

  • implicit: where the interface’s members are directly accessed through the implementing class;
  • explicit: where we have to cast the class to the explicitly implemented interface before we can use it; this is useful, among other reasons, if we want to implement several interfaces which offer identically-named members.

Let’s see how they look in C#, in this example, interface IMyInterface1 is explicitly and IMyInterface2 implicitly implemented:

public class MyClass : IMyInterface1, IMyInterface2

{

    void IMyInterface1.MyMethod1()

    {

    }


    public void MyMethod2()

    {

    }

}

Explicitly-implemented members are always private and cannot be virtual or abstract. If we want to call a method or access a property of an explicitly implemented interface, we need to cast the instance first:

MyClass c = new MyClass();

IMyInterface1 i = (IMyInterface1) c;

i.MyMethod();

Java only has implicit interface implementations:

public class MyClass implements MyInterface

{

    public void myMethod()

    {

    }

}

Inner Classes

In Java as in C#, we can have multiple levels of nested/inner classes, structures and interfaces, but in Java they can be static or instance:

public class MyClass

{

    public static class MyStaticInnerClass

    {

    }


    public class MyInnerClass

    {

    }

}

Instance inner classes can only be instantiated when we have an instance of its containing class (do notice the awful syntax):

MyClass.MyStaticInnerClass c1 = new MyClass.MyStaticInnerClass();


MyClass c2 = new MyClass();


MyClass.MyInnerClass c3 = c2.new MyInnerClass();

In C#, any inner class can be instantiated, with or without an instance of the containing class, provided its visibility level is respected:

public class MyClass

{

    public class MyInnerClass

    {

    }

}


MyClass.MyInnerClass c = new MyClass.MyInnerClass();

For C# the following visibility levels exist:

  • internal: only accessible by other classes in the same assembly (the default);
  • protected: only accessible by descending classes;
  • protected internal: derived classes or classes from the same assembly;
  • private: only accessible by the declaring class;
  • public: accessible by everyone.

Whereas for Java:

  • package: only accessible by other classes in the same package (the default);
  • protected: only accessible by descending classes;
  • private: only accessible by the declaring class;
  • public: accessible by everyone.

Abstract Classes

In Java as in C# we have abstract classes, and the syntax is exactly the same:

public abstract class MyClass

{

    public abstract void myMethod();

}

C# structures cannot be abstract.

Sealed Classes

Both frameworks allow a class to be marked as sealed/final, meaning, it cannot be inherited from:

public sealed class MyClass

{

    //a C# sealed class

}

public final class MyClass

{

    //a Java final class

}

C# structures are always implicitly sealed.

Static Classes

In C# we can have static classes, which are roughly equivalent to being at the same time abstract and sealed. Static classes only allow static members (properties, methods, fields and events):

public static class MyClass

{

    public static void MyMethod()

    {

    }


    public static string MyField;


    public static int MyProperty { get; set; }


    public static event EventHandler MyEvent;

}

Java does not have the concept of static classes.

Nullable Types

Because it is allocated in the stack, a variable of a structure or enumeration type always has a value, so, it cannot be null, but we can use a handy syntax to turn it into a nullable type, which can itself be made null:

int ? nullableInteger = null;

nullableInteger = 1;


if (nullableInteger.HasValue)    //if (nullableInteger != null)

{

    int integer = nullableInteger.Value;    //int integer = nullableInteger

}

In Java, primitive values can never be null, we need to resort to their corresponding wrapper classes:

Integer nullableInteger = null;

nullableInteger = new Integer(1);

Classes and interfaces in C# (reference types) are always nullable, meaning, can always be assigned null.

Partial Classes

C# allows marking a class as partial, meaning, its contents may spread through several different source files; the actual compile-time class will be built from all of these files. This is very useful when we have automatically generated files that we don’t want to change, but rather complement:

//in file MyClass.Generated.cs

public partial class MyClass

{

    public void OneMethod()

    {

    }

}


//in file MyClass.cs

public partial class MyClass

{

    public void AnotherMethod()

    {

    }

}

Anonymous Classes

Java has anonymous classes: we can create anonymous classes that implement some interface or extend some class, by implementing all of its abstract methods:

this.addEventListener(new ListenerInterface

{

    public void onEvent(Object source, Event arg)

    {

    }

});

Anonymous classes in C# do not contain explicitly defined methods, only read-only properties; two anonymous classes are considered of the same type if their members are declared in the same order and with the same types:

var i1 = new { A = 10, B = "" };

var i2 = new { A = 1000, B = "string" };


//these two classes have the same type

i1 = i2;

In order to support anonymous classes, C# introduced the var keyword, which allows us to have a variable infer its type automatically. An anonymous type is created when a variable is created without a static type.

Type Members

In .NET we have the following type members:

  • Constructors (static and instance);
  • Destructors;
  • Methods (static and instance);
  • Fields (static and instance);
  • Properties (static and instance);
  • Events (static and instance);
  • Overridden operators and type conversions (discussed on the next post).

Java only has:

  • Constructors (static and instance);
  • Constructor blocks;
  • Destructors;
  • Methods (static and instance);
  • Fields (static and instance).

Static Constructors

Static constructors or class initializers are basically the same in C# and Java, but have a slightly different syntax, here is the Java one:

public class MyClass

{

    static

    {

        //do something the first time the class is used

    }

}

And the C# syntax:

public class MyClass

{

    static MyClass()

    {

        //do something the first time the class is used

    }

}

Java offers another weird thing: constructor blocks. You can have any number of them, and their code will be included automatically into all of the class’ constructors:

public class MyClass

{

    {

        System.out.println("First constructor block, called before constructor");

    }


    public MyClass()

    {

        System.out.println("MyClass()");

    }


    {

        System.out.println("Second constructor block, called before constructor but after first constructor block");

    }

}

Destructors

In C# a destructor, or finalizer, is just a shorthand syntax to the Finalize method. This method is called by the Garbage Collector when an instance is about to be freed. Java has an identical method, called finalize, which serves a similar purpose. Strictly speaking, none of these methods is actually a destructor, but they are sometimes called that.

In C#, we can use the C++ syntax instead of overriding Finalize:

public class MyClass

{

    ~MyClass()

    {

        //object is being freed

    }

}

Static Members

Unlike C#, Java allows referencing static members through an instance variable, for example:

public class MyClass

{

    public static void doSomething()

    {

    }

}


MyClass c = new MyClass();

c.doSomething();

Properties

Properties are a useful C# construct, which allows a cleaner syntax to changing fields:

public class MyClass

{

    public int MyProperty { get; set; }

}


MyClass c = new MyClass();

c.MyProperty++;

We can have auto-implemented properties (such as in this example) or properties with an explicit backing field:

public class MyClass

{

    private int myField;


    public int MyProperty

    {

        get

        {

            return this.myField;

        }

        set

        {

            this.myField = value;

        }

    }

}

The Java equivalent can only be achieved with methods:

public class MyClass

{

    private int myProperty;


    public void setMyProperty(int value) { this.myProperty = value; }

    public int getMyProperty() { return this.myProperty; }

}


MyClass c = new MyClass();

c.setMyProperty(c.getMyProperty() + 1);

In C# we can also define indexed properties for classes, interfaces and structures, like in this example using an integer index:

public class MyCollection

{

    private Object [] list = new Object[100];


    public Object this[int index]

    {

        get

        {

            return this.list[index];

        }

        set

        {

            this.list[index] = value;

        }

    }

}

We are not limited to integer indexes, any type can be used as the key to an indexed property.

Finally, properties can have different visibility levels for the getter and setter methods, and can even have just one of them (usually just a setter does not make much sense):

public int InternalProperty

{

    get;

    private set;

}


public string GetOnlyProperty

{

    get

    {

        return this.InternalProperty.ToString();

    }

}

Events

Events are C#’s implementation of the Publisher/Subscriber and Observer Patterns: it allows to register methods that will be called when the event is raised, and offers a simple syntax for registering, unregistering and clearing event handlers. An event handler is just an instance of a delegate, the delegate is the event’s signature:

public class MyClass

{

    public event EventHandler MyEvent;


    public void ClearEventHandlers()

    {

        //check for registered event handlers

        if (this.MyEvent != null)

        {

            //raise event

            this.MyEvent(this, EventArgs.Empty);


            //clear event handlers

            this.MyEvent = null;

        }

    }

}


MyClass a = new MyClass();


//register event handler

c.MyEvent += OnMyEvent;


//unregister event handler

c.MyEvent -= OnMyEvent;

Like with properties, it is also possible in C# to implement the event add and remove methods explicitly, so as to add our own behavior:

public class MyClass

{

    private EventHandler myEvent;


    public event EventHandler MyEvent

    {

        add

        {

            this.myEvent += value;

        }

        remove

        {

            this.myEvent -= value;

        }

    }

}

Automatic Initialization of Fields and Properties

All fields declared in a class are initialized to their type’s default value (0 for integers and floating point number, false for booleans, null for classes). C#’s auto-implemented properties are also implicitly initialized to their type’s default value. This behavior is the same in both languages, of course, Java does not have properties.

Member Visibilities

C# has four visibility levels for members:

  • private: accessible from the declaring type;
  • internal: accessible from types in the same assembly as the declaring type;
  • protected: accessible from types inheriting from the declaring type;
  • protected internal: accessible from types either inheriting from the declaring type or from its same assembly;
  • public: accessible by everyone.

And Java, we only have:

  • package: only accessible by classes in the same package;
  • protected: only accessible by descending classes;
  • private: only accessible by the declaring class;
  • public: accessible by everyone.

Virtual Members

In Java, all methods are virtual by default (there is no virtual keyword), unless marked as final.

In C#, a method, property or event needs to be explicitly marked as virtual so that it can be overridden, and all overrides must state so:

public class MyBaseClass

{

    public virtual void MyMethod()

    {

    }

}


public class MyDerivedClass : MyBaseClass

{

    public override void MyMethod()

    {

    }

}

If a derived class member with the same name as one in the base class exists, but it is not an override of it, we need to mark it as new:

public class MyBaseClass

{

    public void MyMethod()

    {

    }

}


public class MyDerivedClass : MyBaseClass

{

    public new void MyMethod()

    {

        //no relation with MyBaseClass.MyMethod

    }

}

Sealed Members

In C# as in Java, it is possible to mark a member (method) as sealed/final, meaning, it is not available for overriding in a derived class. In C# the same applies to events and properties, which, of course, don’t exist in Java.

C# syntax:

public class MyClass

{

    public sealed void DoSomething()

    {

    }

}

And Java syntax:

public class MyClass

{

    public final void doSomething()

    {

    }

}

Abstract Members

In both languages, abstract members (methods) can exist in abstract classes, but they are not required: we can have abstract classes without any abstract members. In C#, besides methods, we can also have abstract properties and events.

Generic Methods

Methods can also be generic, regardless of living in generic classes or not. The same constraints apply, but generic methods also have automatic type inference:

public class MyClass

{

    public static int Compare<T>(T v1, T v2)

    {

        if (v1 == v2)

        {

            return 0;

        }


        return -1;

    }

}


//no need to specify the int parameter type

int areEqual = MyClass.Compare(1, 2);

Read-only and Constant Fields

Both Java and C# have read-only fields, but C# uses the readonly keyword:

public static class Singleton

{

    //a C# readonly field

    public static readonly Singleton Instance = new Singleton();

}

And Java uses final:

public class Singleton

{

    //a Java final field

    public static final Singleton INSTANCE = new Singleton();

}

C# also offers another kind of read-only field, constants. A constant is always static and can only be of one of the primitive types, or an enumerated value:

public static class Maths

{

    //a C# constant field

    public const double PI = 3.1415;

}

The difference between readonly and const is that the C# compiler inlines all constants, that is, it actually replaces any references to it by their concrete values. The Java compiler does something similar for static final fields. Read-only fields can be initialized inline, together with the field declaration, or in constructors (static or instance).

Technical Review

I couldn’t have written this post without the technical review by my friend and colleague Roberto Cortez (@radcortez), of Java fame. Thanks, Roberto! Winking smile

Next Steps

That’s it for now. Stay tuned for the next post, where I will talk about other language differences. Let me hear from you!

Lesser-Known NHibernate Features: Versioning and Optimistic Concurrency

NHibernate supports the notion of entity version. An entity version is the value of some entity property that is mapped as versioned. There are several strategies for versioning:

  • A numeric counter;
  • The current (UTC) timestamp;
  • The database timestamp;
  • The system elapsed ticks (DateTime.Ticks);
  • A database-specific row version (ROWVERSION in SQL Server, ORA_ROWSCN in Oracle, etc).

 

We map a version property as this:

public class VersionedEntity

{

    public int Id { get; protected set; }

    public int Version { get; protected set; }

}


public class VersionedEntityClassMapping<VersionedEntity>

{

    public VersionedEntityClassMapping()

    {

        this.Id(x => x.Id, x => x.Generator(Generators.Identity));

        this.Version(x => x.Version, x => x.Type(NHibernateUtil.Int32));

        //etc

    }

}

If you wish to use a strategy other than auto-incrementing versioning, just replace NHibernateUtil.Int32 by another instance of a class implementing IVersionType, such as NHibernateUtil.Ticks, NHibernateUtil.Timestamp, NHibernateUtil.UtcDateTime, NHibernateUtil.DbTimestamp, NHibernateUtil.Binary (for SQL Server), or a similar one – or roll out your own strategy.

Close to the notion of versioning comes optimistic concurrency. Using optimistic concurrency control, when a record is about to be updated, it is checked against a pre-saved value or set of values (the version), together with its primary key. If it doesn’t match, the number of affected records will be 0 instead of 1, and we know something went wrong: because the primary key doesn’t change, then it has to be the version:

UPDATE some_table

SET some_column = @p1

WHERE id = @p2

AND version = @p3

Optimistic concurrency can use:

  • The version property (if any);
  • All of the entity’s properties;
  • All the dirty properties.

We just need to tell NHibernate which strategy we want to use:

public class VersionedEntityClassMapping<VersionedEntity>

{

    public VersionedEntityClassMapping()

    {

        this.Id(x => x.Id, x => x.Generator(Generators.Identity));

        this.Version(x => x.Version, x => x.Type(NHibernateUtil.Int32));

        this.OptimisticLock(OptimisticLockMode.Version);//NHibernate 4.0, no need to specify since this is the default

        //etc

    }

}

And that’s it. Happy versioning!

Learning Microsoft Azure Review

Introduction

I was recently asked by Packt Publishing to do a review of their title Learning Microsoft Azure, and so I did.

It wasn’t the first time I did a review on an Azure book, I also reviewed Microsoft Azure Development Cookbook, Second Edition, and you can see my review here.

This time, it is an introductory book, where the reader is introduced to Microsoft Azure, and guided as he/she develops a full solution for an imaginary industrial bakery, from end to end, including a mobile app. It covers technologies such as ASP.NET MVC 5, Windows Phone 8, Entity Framework Code First and Web API, always using C# and .NET as the backing framework. At the end of each chapter, there’s a questions and answers page where we can assess our level of understanding of the topics that were discussed in it.

The author is Geoff Webber-Cross (@webbercross), which also authored another book on Azure and Windows Phone.

Chapter 1: Getting Started with Microsoft Azure

The first chapter, as we might expect, does an introduction to cloud computing and the Microsoft Azure service, presents a decision framework for aiding in selecting a cloud service as opposed to on-premises, guides the reader in creating an Azure account including it’s many services and costs, and lists the most relevant terms that we will be encountering throughout the book.

Chapter 2: Designing a System for Microsoft Azure

Here we are presented with the sample scenario, its objectives and requirements and the architectural vision of it. Different views on the system and its subsystems are presented and for each the technical decisions are explained.

Chapter 3: Starting to Develop with Microsoft Azure

Next we setup the development environment, choose a Visual Studio edition, download the required SDK and create a project to be published in our Azure account. Visual Studio Online is also presented and it’s integration with Azure, namely, in order to ensure continuous integration and delivery.

Chapter 4: Creating and Managing a Windows Azure SQL Server Database

Here we get an overview of the SQL functionality of Azure, how to create and manage databases using the portal, Visual Studio and the SQL Server Management Studio, then we learn how to use Entity Framework Code First to access and manipulate its data, and to migrate to and from different versions using the Migrations API.

Chapter 5: Building Azure MVC Websites

This chapter explains how we can build an MVC application using OAuth authentication (social accounts such as Twitter, Facebook, Google and Microsoft Live). It goes on explaining how we can set up custom domains and SSL certificates for HTTPS and how to integrate the Azure Active Directory for single sign-on and custom permissions.

Chapter 6: Azure Website Diagnostics and Debugging

This one is about diagnosing problems and debugging our applications. It presents the basic built-in tracing and logging features of Azure and how we can obtain this information and goes on to show how we can use table storage and blobs for custom storing of structured logs and its querying. Kudu is briefly introduced and at the end we learn how to do remote debugging.

Chapter 7: Azure Service Bus Topic Integration

Next up is Service Bus, Azure’s enterprise service bus service. We learn how to configure it, create and manage topics using the portal and how to use the service from our MVC application and expose it as a service.

Chapter 8: Building Worker Roles

The next chapter is about Worker Roles, a feature of Azure Websites that performs disconnected (non web-related) tasks. The reader is guided in creating a Worker Role with Visual Studio, executing it in the Emulator and publishing it to Azure. The example presented builds on the Service Bus topics discussed in the previous chapter. We also learn about other scheduling mechanism of Azure, Scheduler jobs, and implement an example using Queues.

Chapter 9: Cloud Service Diagnostics, Debugging, and Configuration

Here we learn about configuring and using the diagnostics features of Cloud Services, again expanding the concepts introduced in chapter 6. We talk about IntelliTrace and Remote Debugging and on how to connect to our virtual machines with Remote Desktop. Finally we are given an example on how to use script tasks to automate common needs.

Chapter 10: Web API and Client Integration

This chapter introduces ASP.NET Web API, Microsoft’s latest technology for building REST web services and SignalR, for asynchronous, duplex, real-time communication between web clients and the server. The provided example shows how to integrate these two technologies to broadcast messages to connected clients, including a desktop Windows Presentation Framework (WPF) application. In the end we learn how to use the Active Directory to authorize accesses to our services.

Chapter 11: Integrating a Mobile Application Using Mobile Services

Coming closer to the end, this chapter walks the reader on the various aspects of building a mobile client that connects to the cloud using Azure Mobile Services. We see how to implement a mobile-enabled web application and Web API service, how to publish it and how to implement a matching Windows Phone application, fully featured with push notifications. It also guides us on configuring the mobile service with Active Directory for authentication. At the end we are shown how to build a Windows Store app to interact with our application.

Chapter 12: Preparing an Azure System for Production

The final chapter puts everything in place, explains how to setup different build configurations for different deployment environments and how to build and deliver deployment packages for Azure. At the very end we get a deployment checklist that may come in handy if ever we run into problems.

Conclusion

Overall, I enjoyed reading this book. It doesn’t cover all of Azure, but it does a very decent job in explaining how one can build a real-life application that works and handles most typical concerns, including support for mobile devices.