Introducing SharedFlat


A multitenant web application is one that responds differently depending on how it is addressed (the tenant). This kind of architecture has become very popular, because a single code base and deployment can serve many different tenants.

There are a few libraries out there that help ASP.NET Core developers implement such architectures, but, since I wrote a book on ASP.NET Multitenant Applications a few years ago, I decided to write something from scratch for ASP.NET Core – and here is SharedFlat!

For the sake of the examples, let’s assume two tenants that correspond to two different domain names, (abc) and (xyz).


SharedFlat is available at GitHub and NuGet and you are free to have a look, fork and suggest improvements. It is still in early stages, mind you!

It was designed around the following key tenets:

What is a tenant?

A tenant is a unique entity, identified by a name, and the application must respond appropriately to in, in terms of:

  • User interface: each tenant may have one or more different UI aspects
  • Data: each tenant should have access to different data
  • Behavior: the application should behave (maybe slightly) differently, for each tenant

The current tenant is always returned by the implementation of the ITenantService interface:

public interface ITenantService


string GetCurrentTenant();


Simple, don’t you think? The returned tenant information is the tenant’s name (or code, if you prefer).

How do we identify a tenant?

Now, the first thing to know is, how do we identify the current tenant? Well, there are different strategies for this, but they all implement this interface:

public interface ITenantIdentificationService


string GetCurrentTenant(HttpContext context);


The strategies itself can be various:

  • Using the request’s HTTP Host header: useful for scenarios where we have multiple domains pointing to the same IP address and we want to distinguish the tenant by the requested host
  • Using a query string field: more for debugging purposes
  • Using the source IP of the request: for when we want to force IPs to be of a specific tenant
  • Static: for testing purposes only
  • Dynamic: when we decide in code, at runtime, what the tenant is
  • Some header’s value


The ITenantService that we saw first will have to somehow delegate to one of these implementations for getting the current tenant. We need to register one implementation by using one of the following extension methods:


.DynamicTenant(ctx => “”) //dynamic

.TenantForQueryString() //query string

.TenantForSourceIP() //source IP

.TenantForHost() //host header

.TenantForHeader() //some header

.StaticTenant(“”); //static

Of course, only one of these methods (DynamicTenant, TenantForQueryString, TenantForSourceIP, TenantForHost, TenantForHeader, StaticTenant) should be called.

Some of these different strategies need configuration. For example, to map a host name to a tenant name, we use code like this:


.TenantForSourceIP(options =>


options.Mapping.Default = “abc”;


.Add(“”, “xyz”)

.Add(“”, “abc”);


Some tenant identification services also expose an interface ITenantsEnumerationService, which allows listing all the known tenants (their name, or code). This service can be retrieved from the DI, but only if the registered identification service supports it:

public IActionResult Index([FromServices] ITenantsEnumerationService svc)


var tenants = svc.GetAllTenants();

return View(tenants);


Configuration per tenant

It is also very important to get different configuration depending on the current tenant. Almost all of the tenant identification strategies (except StaticTenantIdentificationService and DynamicTenantIdentificationService) support a mapping between “something” and a tenant code. This “something” may be the source IP (SourceIPTenantIdentificationService), the request’s Host header (HostTenantIdentificationService), etc. There is a standard configuration section that you can add to your appsettings.json file:


“Tenants”: {

“Default”: “”,

“Tenants”: {

“”: “xyz”,

“”: “abc”




You can load the configuration using an extension method:


.TenantForHost(options =>




Or you can just set the values manually, as we’ve seen before.

If you want to set some per-tenant configuration, you should use the Options Pattern with a named configuration (one per tenant):

services.Configure<SomeClass>(“abc”, options =>


options.Foo = “bar”;


And then you need to retrieve it like this:

public HomeController(IOptionsSnapshot<SomeClass> optionsSnapshot, ITenantService tenantService)


var tenant = tenantService.GetCurrentTenant();

var options = optionsSnapshot.Get(tenant);



There is yet another option: you can have a class that implements ITenantConfiguration, which is defined as:

public interface ITenantConfiguration


string Tenant { get; }

void ConfigureServices(IConfiguration configuration, IServiceCollection services);


You can have one class per tenant and in there you can register services that are specific for it. In order for it to work, you need to call the AddTenantConfiguration extension method:


.TenantForHost(options =>






This is all I have for now, stay tuned for more on SharedFlat!

Modern Web Development with ASP.NET Core 3 – Second Edition

Modern Web Development with ASP.NET Core 3 - Second Edition

So, my new book is out now! The title changed recently from Mastering ASP.NET Core 3 – Second Edition to Modern Web Development with ASP.NET Core 3 – Second Edition. It was Packt’s decision, and I didn’t really bother about that, although I think the former was more accurate. It’s around 700 pages, and it is divided in three parts:

  • The Fundamentals of ASP.NET Core
  • Improving Productivity
  • Advanced Topics

On the first part, we can find the following chapters:

  1. Getting started with ASP.NET Core
  2. Configuration
  3. Routing
  4. Controllers and Actions

On the second part, we have:

  1. Using Forms and Models
  2. Implementing Razor Pages
  3. API Controllers
  4. Reusable Components
  5. Understanding Filters
  6. Security

Finally, on the third and last:

  1. Logging, Tracing, and Diagnostics
  2. Understanding How Testing Works
  3. Client-Side Development
  4. Improving Performance and Scalability
  5. Real-Time Communication
  6. Introducing Blazor
  7. gRPC and Other Topics
  8. Application Deployment

There is also an appendix on the dotnet tool.

I’d say the highlights are:

  • Configuration and feature management
  • API controllers including versioning and OData
  • Razor Pages
  • SignalR
  • Blazor
  • gRPC

The technical reviewers were Alvin Ashcraft (Microsoft MVP and world famous for Morning Dew) and Prakash Tripathi (Microsoft MVP too).

Should you wish to buy it in the next days, there is a discount code that you can use that will grant you a 50% discount: WEBDEV50.

I hope you enjoy it and I’d like to hear from you about the book! Winking smile

ASP.NET Core OData Part 3


This will be the third post on OData and ASP.NET Core 3. Please find the first post (basics) here and the second post (querying) here. This time, I will talk about actions and functions. For demo purposes, let’s consider this domain model:



A function in OData is like a pre-built query that may take some parameters and either return a single value or a collection of values, which may be entities. An action is similar, but, unlike functions, an action can have side effects, that is, it can make modifications to the underlying data.

Some examples of function calls might be

  • /odata/blogs/FindByDate(date=2009-08-01) – returning a collection of entities
  • /odata/blogs/CountPosts(blogid=1) – returning a single value
  • /odata/blogs/Blog(1)/Count – returning a single value
  • /odata/CountBlogPosts – returning a single value

As you can see in these example links, most of them are associated with the “blogs” entity set, these are called bound functions, but one of them is not, it is therefore an unbound function.

Registering these functions can be a bit tricky because there are a few things involved:

  • The [ODataRoutePrefix] attribute in a controller
  • The way we define the function when we build the EDM Data Model
  • The [ODataRoute] applied to the action method

But I digress. Let’s start with the first function.

Bound Function with Parameters Returning a Collection of Entities

For this we need to define a function in our model, associated with an entity set:

var findByCreation = builder
findByCreation.ReturnsCollectionFromEntitySet<Blog>("Blogs"); findByCreation.Parameter<DateTime>("date").Required();

This will register a function named FindByCreation in the Blogs entity set, which returns a collection of Blog entities and takes a parameter of type DateTime named date.

Its implementation in a controller is:

public class BlogController : ODataController
    private readonly BlogContext _ctx;

    public BlogController(BlogContext ctx)
this._ctx = ctx;

    public IQueryable<Blog> FindByCreation(DateTime date)
        return _ctx.Blogs.Where(x => x.Creation.Date == date);

Notice the Blogs prefix applied to the BlogController class, this ties this class to the Blogs entity set.

The [EnableQuery] attribute, discussed on the previous post, allows the results of this function to be queried too.

Now you can browse to https://localhost:5001/odata/blogs/FindByCreation(date=2009-08-01) and see the results!

Bound Function with Parameters Returning a Single Value

Another example, this time, returning a single value:

var countPosts = builder


The function CountPosts is registered to the Blogs entity set, taking a single required parameter named id.

As for the implementation, in the same BlogController:

public int CountPosts(int id)
    return _ctx.Blogs.Where(x => x.BlogId == id).Select(x => x.Posts).Count();

This will be available as https://localhost:5001/odata/blogs/CountPosts(id=1)

Unbound Function

Next up, an unbound function, that is, one that is not associated with an entity set:

var countBlogPosts = builder.Function("CountBlogPosts");

This function, as you can see, is not attached to any entity set.

Its implementation must be done in a controller that is also not tied to any entity set (no [ODataRoutePrefix] attribute):

public class BlogPostController : ODataController
private readonly BlogContext _ctx;

public BlogPostController(BlogContext ctx)
this._ctx = ctx;

    public int CountBlogPosts()
return _ctx.Posts.Count();

And to call this function, just navigate to https://localhost:5001/odata/CountBlogPosts().


The difference between actions and functions is that the former may have side effects, such as modifying data. It should come as no surprise, following REST principles, that actions need to be called by POST or PUT. Let’s see a couple examples

Bound Function with Key Parameter and No Payload Returning a Single Value

Here we want the URL to reflect the fact that we are invoking this function on a specific entity. The definition of the function in the EDM Data Model is:

var count = builder
count.Parameter<int>("id").Required(); count.Returns<int>();

Now we are using Action instead of Function to define the Count action!

As for the definition:

public int Count([FromODataUri] int id)
    return _ctx.Blogs.Where(x => x.BlogId == id).Select(x => x.Posts).Count();

Notice that we applied the [FromODataUri] attribute to the id parameter, this is required.

To call this action, you will need to POST to https://localhost:5001/odata/blogs/Blog(1)/Count.

Bound Function with Key Parameter and Payload Returning an Entity

The difference between this one and the previous is that this receives an entity as its payload. The definition first:

var update = builder


Notice how I replaced Parameter by EntityParameter.

The action method implementation is:

public Blog Update([FromODataUri] int id, ODataActionParameters parameters)
var blog = parameters["blog"] as Blog;
_ctx.Entry(blog).State = EntityState.Modified;
    return blog;

And to call this, you need to POST to https://localhost:5001/odata/blogs(1)/Replace with a payload containing a blog property with a value that is the Blog that you wish to update:

    "blog" : {
        "BlogId": 1,
        "Name": "New Name",
        "Url": "http://blog.url",
        "CreationDate": "2009-08-01"


This concludes the topic of functions and actions. On the next post I will be talking about some more advanced features of OData.

ASP.NET Core OData Part 2

Update: see the third post here.


This is the second post on my series on using OData with ASP.NET Core 3. You can find the first here.


We’ve seen how we can expose an object model to OData. In the first post I used Entity Framework Core, but you don’t need to use any ORM.

Where OData really excels is in querying: you can perform LINQ-style queries over the URL. These include:

  • Filtering
  • Sorting
  • Projections
  • Pagination
  • Counting
  • Navigation property expansions

By default, when you access the entity set’s endpoint, you get all records, but you can enable querying over them. This needs to be done globally first, when you define the endpoint:

app.UseEndpoints(endpoints =>
    endpoints.MapODataRoute("odata", "odata", GetEdmModel(app.ApplicationServices));

Let’s have a look at the extension methods after the route registration. Don’t worry, I will show examples in a moment.

  • The Select extension method allows projections over an entity, that is, selecting only parts of it
  • Expand is used to allow expansions, for example, while retrieving an entity, similar to what Include does in Entity Framework Core – in fact, it translates to it
  • OrderBy is self explanatory. without it you won’t be able to sort the results of your query
  • Filter is what permits querying
  • Finally, Count is used to allow returning only the count, not the actual results

These are global settings, but we also need to enable them at the configuration, per entity, when we build the EDM Data Model (the GetEdmModel method I’ve shown previously):


Finally, we also need to enable it in the action method that returns a query (IQueryable<T>), regardless of whether or not it is wrapped in an IActionResult:



public IQueryable<Parent> Get()

Once we do this, we can now query the entity set on the URL, but first, we need the [EnableQuery] attribute. This is what allows us to query over the results!

If you don’t want to decorate all your action methods with [EnableQuery], we can also do this globally, for any queryable action methods:


This has the advantage (or disadvantage) that it applies to all methods, unless we specifically tell OData that querying is not allowed.

As for querying, we have a number of options, I’m going to show just the simplest:

Filter by a property’s value:

/odata/Parents?$filter=Name eq ‘Ricardo Peres’

Sort by one property’s values descending:

/odata/Parents?$orderby=Name desc

Select just a single property:


Skip 10 records and retrieve the next 5, ordered by a property:


Filter by a property’s value and return the count:


Expand a collection property:


The main keywords are:

  • $filter: used for specifying conditions
  • $orderby: for sorting, either ascending or descending
  • $select: projections
  • $top: getting only some records
  • $skip: skipping some records
  • $count: getting the count of the returned records together with them
  • $expand: expansions (include navigation properties)

Some of the options can be enhanced, for example:

Filter by several conditions:

/odata/Parents?$filter=Id eq 1 or Id eq 2

/odata/Parents?$filter=Id eq 1 and Name eq ‘abc’

Where property value is in list:

/odata/Parents$filter=Id in (1, 2)

Sort by two property’s values, one descending and the other ascending:

/odata/Parents?$orderby=Name desc,Id asc

Filtering an expansion:

/odata/Parents?$expand=Children($filter=Name eq ‘A Child’)

I won’t go through all of the possible expressions, but the full OData specification is available here.

Setting Limits

We’ve seen in the beginning, while defining the OData route, that we can tell OData what should it support (select, filter, orderby, expand). We can also define the maximum amount of records to return:

app.UseEndpoints(endpoints =>
    endpoints.MapODataRoute("odata", "odata", GetEdmModel(app.ApplicationServices));

Notice the MaxTop extension method, it defines the global maximum amount of records that can be returned by an OData endpoint. But we can also configure it on the action method, using the [EnableQuery] attribute:


[EnableQuery(MaxTop = 10)]

public IQueryable<Parent> Get()

The [EnableQuery] attribute allows you to define a lot of other restrictions:

All of these options can also be specified through the AddODataQueryFilter extension method, but for global restrictions. It is at least advisable to define a maximum number of return records (MaxTop) and also the maximum number of expansions (MaxExpansionDepth).

Return Result

Querying will work both if you are returning an IQueryable<T> collection or an IEnumerable<T>. The thing is, with the former, your query will be executed in the server (the database), whereas with the latter, it will be executed in memory (LINQ to Objects). You will still be able to query, but it won’t be the same!

Inspecting Query Options

In your action methods, whenever querying is allowed, we have a way to get the query options passed to the URL ($filter, $orderby, etc), and then choose whether or not we want to apply them. The key lies in the ODataQueryOptions<T> class:

public IQueryable<Parent>Get(ODataQueryOptions options)
if (options.Top != null && options.Top.Value == 0) { options.Top.Value = 10; } var parents = _ctx.Parents.AsQueryable(); parents = options.ApplyTo(parents) as IQueryable<Parent>; return parents;

Here you can inspect the current filter (Filter), sort order (OrderBy), expand (SelectExpand), skip (Skip), count (Count) and even make changes. When you’re happy with then, just ApplyTo a base queryable collection.


This covers the basic querying options of OData. In the next post, functions and actions!


Please refer to the following links for additional information:

Mastering ASP.NET Core 3.0 – Second Edition

Mastering ASP.NET Core 3.0 - Second Edition

My new book, Mastering ASP.NET Core 3.0 – Second Edition, for Packt Publishing, will be available from June 19. It is a almost total rewrite from my previous one, Mastering ASP.NET Core 2.0, and it covers all of the goodies that ASP.NET Core 3.0 and 3.1 brought along. I cover Razor Pages, Blazor, OData, gRPC and some less-known features as well.

For personal reasons, it was difficult to write, and, in fact, it should have come out long ago, but, if we think about it, if it had, I wouldn’t have had the chance to cover some technologies – such as Blazor WebAssembly – that were only released recently.

I will come back to this with more information, including the table of contents, soon.

In the end, I can say that I am happy with the result, and hope you, dear readers, enjoy it too!

ASP.NET Core OData Part 1

Update: see the second post here.


OData is an open standard for making an object-oriented domain model available as an HTTP REST interface.In a nutshell, it provides a specification for returning domain models as result of HTTP requests, querying them over the URL and even creating functions and actions over the domain model. In what .NET Core is concerned, it is a way by which you can expose your Entity Framework Core – or any other ORM that has a LINQ interface – to the web, without writing too much boilerplate code, as an ASP.NET Core Web API.

It is surprising that not many people know about OData, also, there are some caveats to it and not much documentation on using it with ASP.NET Core, so I decided to write a few posts on the subject. Here is the first!

Setting Up

Let’s pretend you have a domain model with just two classes, Parent and Child:


We should also have an Entity Framework Core context that exposes them:

public class ParentChildContext : DbContext


public ParentChildContext(DbContextOptions options) : base(options) { }

public DbSet<Parent> Parents { get; set; }

public DbSet<Child> Children { get; set; }


I won’t go into details as to explain this, I’m pretty sure you all know about Entity Framework Core contexts! Just make sure you add a reference to the Microsoft.EntityFrameworkCore NuGet package, or, if you’re using SQL Server, Microsoft.EntityFrameworkCore.SqlServer. Now register your context to the DI framework, in the ConfigureServices method:

services.AddDbContext<ParentChildContext>(options =>


options.UseSqlServer(“<connection string>”);


In your ASP.NET Core’s project you need to add a reference to the Microsoft.AspNetCore.OData NuGet package. This includes the server-side implementation of OData version 4 for ASP.NET Core.

You need to add its required services in the ConfigureServices method:


This registers the services, but now we need to add an endpoint for an actual domain model. ASP.NET Core OData now supports endpoint routing, so everything can be done smoothly:

app.UseEndpoints(endpoints =>

{ endpoints.MapODataRoute(“odata”, “odata”, GetEdmModel(app.ApplicationServices)); });

We registered this endpoint with name odata (first parameter) and also with the same prefix (second parameter), you can happily change this. As you can see, in this route, we are returning an EDM Data Model. We build one as this:

private static IEdmModel GetEdmModel(IServiceProvider serviceProvider)


var builder = new ODataConventionModelBuilder(serviceProvider);



return builder.GetEdmModel();


One thing that you’ll notice is that this is a conventions-based model builder, ODataConventionModelBuilder. this one takes care of some things for you, such as inferring the id property for each entity, that’s why you don’t have to explicitly state it. If your entity has an id property with a funny name, other than Id or EntityId, then you will need to specify it:




.HasKey(x => x.Id);

There is no need to specify the other properties, because they are all inferred automatically too from the generic parameter.

Do keep in mind the entity set name that you give, it is common to have a pluralized form of the entity name, but it is not required.

Now we need to create a controller that exposes this. At the very least, we will need two methods:


public class ParentController : ODataController


private ParentChildContext _ctx;

public ParentController(ParentChildContext ctx)


this._ctx = ctx;



public IQueryable<Parent> Get()


return this._ctx.Parents.AsQueryable();



public Parent Get([FromODataUri] int id)


return this._ctx.Parents.Find(id);



This controller is specific to the Parents entity set, so, if you wish, you need to have another one for the Children. This is specified in the [ODataRoutePrefix] attribute.

Also notice how we are returning IQueryable<Parent> from the Get action method that does not take parameters and a single Parent from the other. You can also declare IActionResult or ActionResult<T>:


public IActionResult Get()


return this.Ok(this._ctx.Parents.AsQueryable());




public ActionResult<IQueryable<Parent>> Get()


return this.Ok(this._ctx.Parents.AsQueryable());


The latter, the one that uses ActionResult<T>, has some advantages, which you can read about here.

And, of course, all of the methods can be made asynchronous too:


public async Task<IQueryable<Parent>> Get()


return await this._ctx.Parents.ToListAsync();



public async Task<Parent> Get([FromODataUri] int id)


return await this._ctx.Parents.FindAsync(id);


We will see a problem with the implementation of the first method in the next post.

Now, the first method, the one without parameters, returns all of the entities in the database, and the second, as one would expect, returns possibly one from its id property.


We’re all done here, so we can now access the endpoints we just created, try to navigate to the following URLs:

  • /odata: returns information about the exposed entity sets (Parents and Children)


  • /odata/parents –> ParentController.Get(): returns all records for the Parent entity
  • /odata/parents(1) –> ParentController.Get(1): returns possibly one record, if it exists in the database for the given primary key of the Parent entity

This is the very basics, in the future posts we will explore other options, such as querying over the URL and creating functions and actions.


You can find more information in the following pages:

Dynamic Payloads in ASP.NET Core

It has always been possible (but a tad problematic) to submit dynamic contents to an ASP.NET Core controller action. In the dark, pre-Core days, we had to implement a custom model binder for this. Now it is no longer the case.

All we need is to declare an action method as having a dynamic parameter, obtained from the request body, and accepting the request through POST:

public IActionResult Post([FromBody] dynamic payload)
    return Json(new { Ok = true });

This will accept any content that we POST, if we use the Content Type application/json, and it will by default be turned into a System.Text.Json.JsonElement, a type of the new JSON API, which is the default serializer of ASP.NET Core 3.

If, for some reason, we want to go back to the previous serializer, JSON.NET (Newtonsoft.Json), we need to do a couple of things:

  1. Install the Microsoft.AspNetCore.Mvc.NewtonsoftJson Nuget package (it will bring all of the necessary dependencies)
  2. Configure it as the default serializer (AddMvc or AddControllers or AddRazorPages or AddControllersWithViews all allow this):




If you do, the payload will instead by a Newtonsoft.Json.Linq.JObject instance. The main difference between the two serializer is outlined here. In the end, System.Text.Json supports most of the usual cases and is already included.

In general, I prefer using strongly-typed models, but there may be use cases for this, particularly when implementing routers, API gateways or similar functionality.

As always, hope this is useful! Smile

Unit Testing the HttpContext in Controllers


When it comes to unit testing, it is common to use mocking to replace “external” services, that is, those that are not part of the subject under test. Not everything can be mocked, and, sometimes, when we instantiate non-POCO classes, such as controllers (ControllerBase), there are lots of things that are not instantiated by the framework and are left for us do to. Just think, for example, if you want to access request or quest string data or know if the user is logged in?

In this post I will talk about two things: the user identity and the request data.

The HttpContext

Inside of a controller action method, it is common to get information which actually comes from the the context (the HttpContext property):

All of these properties get routed to the HttpContext property, which is read-only. It turns out that this property is itself routed to the ControllerContext’s property’s own HttpContext, but the ControllerContext can be set:

var controller = new HomeController();
controller.ControllerContext = new ControllerContext();

So, if we want to set a controller’s HttpContext property, all we have to do is set the ControllerContext’s HttpContext:

controller.ControllerContext.HttpContext = new DefaultHttpContext();

The DefaultHttpContext class is the default implementation of the abstract HttpContext class that is included in ASP.NET Core.


All of the .NET and ASP.NET Core is very modular and designed for extensibility, so it should come as no surprise that all of the HttpContext features are provided as features and it’s easy to provide implementations for them.

Features are accessible through the Features collection and can be set using as key one interface, which is generally a core interface that identifies that feature:

context.Request.Set<IFormFeature>(new FormCollection(request));

The DefaultHttpContext takes in one of its constructors a collection of features, from which it can extract its functionality.

Request Data

When we talk about the request we can be talking about:

  • Form data (including files)
  • The query string

Each is implemented by its own feature. So, if we want to mock form data, we would do something like this, leveraging the IFormFeature:

var request = new Dictionary { { “email”, “” }, { “name”, “Ricardo Peres” } }; var formCollection = new FormCollection(request); var form = new FormFeature(formCollection);

var features = new FeatureCollection(); features.Set<IFormFeature>(form); var context = new DefaultHttpContext(features);

This allows us to write code like this, from inside the :

var email = HttpContext.Request["email"];

As for the query string, we would do it like this, using IQueryFeature:

var request = new Dictionary { { “id”, “12345” } }; var queryCollection = new QueryCollection(request); var query = new QueryFeature(queryCollection);

var features = new FeatureCollection(); features.Set<IQueryFeature>(form); var context = new DefaultHttpContext(features);

This code gives us the ability to do this:

var id = HttpContext.Request.Query["id"];


What about sending responses, HTTP status codes and cookies? I’ve got you covered too! The feature contract for the response is IHttpResponseFeature and we add it like this:

var response = new HttpResponseFeature();

var features = new FeatureCollection(); features.Set<IHttpResponseFeature>(response); var context = new DefaultHttpContext(features);

var responseCookies = new ResponseCookiesFeature(context.Features);

Notice that the ResponseCookiesFeature is a little awkward, as it takes the feature collection in its constructor.

With this on, you can set the response status or some cookies on the response of your action:

Response.StatusCode = 400;
Response.Cookies.Append("foo", "bar");

User Identity

As for the user identity, it’s much simpler, we just need to create a ClaimsPrincipal with any claims that we want:

var context = new DefaultHttpContext(features)

{ User = new ClaimsPrincipal(new ClaimsIdentity(new Claim[]


     new Claim(ClaimTypes.Name, “<username>”),

new Claim(ClaimTypes.Role, “<role>”)

    })) };

You can just pass any username and roles you want, and they will be made available to the controller’s User property.


As you can see, with a little bit of work, almost anything is possible in .NET Core, and, particularly, when it comes to unit tests! Stay tuned for more! Winking smile

Dynamic Routing in ASP.NET Core 3

ASP.NET Core 3 introduced a not so talked about feature which is dynamic routing. In a nutshell, it means that it is possible to decide at runtime the controller, action and route tokens that a request will be dispatched to. The idea is to map a route pattern to a dynamic route handler, like this:

app.UseEndpoints(endpoints =>

This maps a route of “/search/<anything>” to a class SearchValueTransformer, which is then responsible for supplying values for the controller and action.

This SeachValueTransformer class must inherit from DynamicRouteValueTransformer, this is the abstract base class for all dynamic route handling, and it only has one method to implement, TransformAsync. The example I am providing here is that of a service that receives some random query for a product on the URL and then decides to which controller it will be forwarded to. A sample implementation of this class would be:

class SearchValueTransformer : DynamicRouteValueTransformer { private readonly IProductLocator _productLocator; public SearchValueTransformer(IProductLocator productLocator) { this._productLocator = productLocator; } public override async ValueTask TransformAsync(

HttpContext httpContext, RouteValueDictionary values) { var productString = values[“product”] as string; var id = await this._productLocator.FindProduct(“product”, out var controller); values[“controller”] = controller; values[“action”] = “Get”; values[“id”] = id; return values; } }

As you can see, it takes an instance of an IProductLocator (I will get to that in a moment) in its constructor, which means that it supports dependency injection. The TransformAsync extracts a “product” parameter from the route – I am skipping validation because if we got here that’s because we matched the route – which it then uses to call the stored IProductLocator instance to retrieve the id and controller, which are then set as route parameters. The result route is then returned.

The SearchValueTransformer needs to be registered in the dependency injector too:


The actual lifetime is irrelevant, here I am setting it as singleton because the SearchValueTransformer holds a single IProductLocator which is itself a singleton and nothing else.

As to the IProductLocator, here is it’s interface:

public interface IProductLocator
    Task<string> FindProduct(string product, out string controller);

The actual implementation, I leave it up to you, it must apply some logic to the product passed in the URL to decide which controller should be used for search it, and then return some reference and a controller responsible for returning information about it. This interface and its implementation must also be registered:

services.AddSingleton<IProductLocator, ProductLocator>();

And this is it. This may serve as a complement to static routing, other uses include translating route parts (controller, action) on the fly. As always, hope you find this useful!

Performance in .NET – Part 4


This is my fourth post on performance in the .NET world. See the first one on object instantiation here and the second on property copying here and the third here. This time I’m going to talk about collections, but focusing on the performance side.This time, I’ll be talking about value types.

Value Types versus Reference Types

Value types – structs and enums – are always allocated in the stack, as opposed to reference types – classes – , which are allocated in the heap. This means that value types are automatically released from memory when they go out of scope – end of the block/method where they are declared, or the class is garbage collected, which is more rare. Value types are thus cheaper to create and do not need to be checked by the garbage collector.

Some aspects, though, need attention.

Instance Comparison

When you compare two value types using the Equals method, if there is no override for it, the value type is compared byte by byte. This is, as you can image, pretty inefficient. Is is recommended that you implement your own Equals (and GetHashCode too) and also that you implement IEquatable<T> interface for comparing two instances of your value type without incurring into boxing and unboxing.

Usage in Lists

Storing value types in array-based lists that permit reordering (random insertions and deletions), such as List<T> is painful, because of the items need to be copied, and copying for value types means byte by byte copying. Avoid if possible.

Usage in Arrays

Value types are great for usage in arrays, because a value type has no object header, so it’s size in memory is very small. The size of the array is therefore small when compared to the same array of reference types.


Do use value types as much as possible, but stay aware of the problems. As always, looking forward to hearing your thoughts. I’ll be back for more.