Deborah's Developer MindScape

         Tips and Techniques for Web and .NET developers.

May 11, 2016

Angular 2: Getting Started with a Visual Studio 2015 ASP.NET 4.x Project

My “Angular 2: Getting Started” course on Pluralsight details how to get started with Angular 2. To provide guidance that works on any platform (Windows, OS X, and Linux), the course uses Visual Studio Code as the editor. However, there are many developers that prefer to use Angular 2 with Visual Studio 2015.

The biggest challenge in providing guidance for using Angular 2 with Visual Studio 2015 is that there are too many options as outlined in this prior post. This post focuses on using Angular 2 with a Visual Studio 2015 ASP.NET 4.x project.

NOTE: If you don’t want to follow all of these steps, you can download the “Angular 2: Getting Started” starter files for an ASP.NET 4.x project in Visual Studio 2015 here: and use the “APM – Start VS 2015 ASP 4x” folder. The only step required below is then Step #2, downloading and installing the latest TypeScript tools for Visual Studio 2015. When you first open the provided solution, the packages will install/update automatically.

To manually set up and run the “Angular 2: Getting Started” files using a ASP.NET 4.x project in Visual Studio 2015, follow these steps:

1. Download the Angular 2 starter files from my GitHub repo:

    If you are not familiar with using GitHub, just click on the “Download ZIP” button as shown below. Then unzip the files.


2. Open Visual Studio 2015 and download the latest set of TypeScript tools for Visual Studio. Open Tools | Extensions and Updates and search for TypeScript. Select the latest TypeScript version (1.8.4 shown below). Then install the downloaded package.


3. Create a new project: File | New | Project, select the ASP.NET project template and name the project “APM” for Acme Product Management.


4. Select the desired ASP.NET 4.x template. I selected the empty template with no MVC, no authentication and no hosting.


5. Copy the files from the APM – Start folder that was downloaded from my GitHub repo (see Step #1) to the APM folder containing the APM.csproj folder.


6. Select the Show All Files button in Solution Explorer to show all of the files.


7. Right-click on each folder/file to be included in the project (as shown below) and select ‘Included in Project’.

NOTE: You may see a dialog that asks if you want to search for TypeScript Typings. Select ‘No’.


8. Right-click on packages.json and select ‘Restore Packages’. This uses npm to install all of the packages defined in the package.json file. (Similar to typing ‘npm install’ at a command line prompt.)


9. Open the Output window (View | Output) to watch the npm command execute. When it is finished, you should see something like this:


NOTE: If you are using Angular 2 RC or higher and see errors here, such as: “‘angular/compiler’ is not in the npm registry”, your Visual Studio 2015 is most likely using an older version of npm. To correct this. Use Tools | Options | Projects and Solutions | External Web Tools and move the $(PATH) entry above the $(DevEnvDir) entries as shown below.


10. Refreshing Solution Explorer, you should then see a node_modules and typings folders as hidden folders for the project.


11. There is one additional option in the tsconfig.json file that is not required when using VS Code or some of the other editors, but is required if using Visual Studio 2015. Add this line to the tsconfig.json file: “compileOnSave” = true and SAVE.


You may have better results at this point if you exit Visual Studio 2015 and reopen it.

12. Click the Run button or press F5 to run the application.

This will launch your default browser and run the application. You can then edit any of the project files (AND SAVE!). Then refresh the browser to see your changes. NOTE: The refresh only works when there is no routing path in the address bar.

13. If you see errors on compilation such as “Property ‘map’ does not exist on type ‘Observable<Response>’” or “Observable cannot be found”, then exit Visual Studio and follow the instructions here:

This involves replacing your C:\Program Files (x86)\Microsoft Visual Studio 14.0\Common7\IDE\CommonExtensions\Microsoft\TypeScript.typescriptServices.js file. NOTE: This requires admin privileges.

By following the above steps, you can follow along with the course using Visual Studio 2015 instead of VS Code.

It would be great to hear from you on whether these steps worked for you. Follow me on twitter: @deborahkurata


April 28, 2016

Angular 2: Getting Started With Visual Studio 2015

My “Angular 2: Getting Started” course on Pluralsight details how to get started with Angular 2. To provide guidance that works on any platform (Windows, OS X, and Linux), the course uses Visual Studio Code as the editor. However, there are many developers that prefer to use Angular 2 with Visual Studio 2015.

The biggest challenge in providing guidance for using Angular 2 with Visual Studio 2015 is that there are too many options.

  • Do we use TypeScript? If so, do we use a TypeScript project in Visual Studio 2015?
  • Do we use a simple “Web Site”?
  • Do we use ASP.NET? If so, ASP.NET version 4.6 (current version) or ASP.NET Core 1.0 (previously known as ASP.NET version 5.0 and currently in beta)
  • Do we use MVC? If so, MVC 5 (current version) or MVC 6 (currently in beta)?
  • Do we use more JavaScript-ish tools such as npm? Or try to do everything with Visual Studio tools?
  • Do we use the command line? Or try to do everything within the Visual Studio 2015 IDE?
  • And so on …

The plan is to cover several of these options, starting with the most basic steps required to use Visual Studio 2015 with Angular 2.

Here are the links to the options covered so far:


April 4, 2016

“Angular 2: Getting Started” Problem Solver

This blog post supports the sample code for the “Angular 2: Getting Started” course on Pluralsight, identifying common issues along with their solutions. This course was updated on October 18, 2016 for the final release of Angular 2.

The content of this post is based on Angular version >= 2.x unless explicitly stated otherwise.

The sample code can be found here: The folders in this repo include:

  • APM – Start: The starter files. Use this as a starting point to code along with the course.
  • APM – Final: The completed files, updated to Angular 2 Beta 15. This code matches with the demos presented in the course.
  • APM–Start-Updated: The starter files, updated to Angular 4.
  • APM–Final-Updated: The completed files, updated to Angular 4.

Please post to the Discussion tab for the course if you experience an issue not found in this post. Thanks!


npm Issues

Problem: Error when using `npm install`.

There are several possible solutions depending on the source of your problem.

Solution 1: Ensure you have a current version of npm installed. The course was tested with node v6.5.0 and npm 3.10.6. If your version is significantly older, it may not work. Use node –v and npm –v to check your versions. To install a newer version of both tools, use this link:

Solution 2: It may be a permissions problem. Try the steps found here:


Setting Up Behind a Corporate Web Proxy

Problem: Error in installing typings when performing `npm install`. Error may be something like “Failed at the product-management@1.0.0 postinstall: ‘typings install’

Solution 1: npm may not be using your globally defined proxy setting. Try adding a .typingsrc file with the value: "proxy="

Solution 2: Try manually installing the typings by running the following command at the command prompt: `npm run typings install`

Solution 3: Try the updated version of the starter files: APM-Start-Updated. Later versions of Angular 2 changed how the types are accessed and using these newer versions often prevent some of the typings issues.

See these posts for more information:

NOTE: If the proxy requires authentication (which is usually true), please use this format

$ npm config set proxy http://login:pass@host:port
$ npm config set https-proxy http://login:pass@host:port

NOTE: If you do not have access to the proxy URL and port, you can install the missing typing manually following the steps posted by Joe Ballard in the comments for this post below. Note however that with Angular 2 final you need core-js and node NOT es6-shim. See the typings.json file for details.


Can I Follow the Course Without Installing Node?

Problem: Some viewers can’t install node due to limitations on installation of external apps or proxy issues. In this case, it still possible to code along with the course.

Solution: Use Plunker! Plunker is a playground that allows you to work with JavaScript, TypeScript, and Angular without downloading or installing anything.

To use Plunker:

1) Access the Web site:

2) Select "Launch the Editor" (big blue button in the upper left).

3) Drop down the list from the New button (big green button in the toolbar) and select Angular. (A box appears telling you that you have unsaved changes. Just click Yes to proceed)

This sets up everything you need to run Angular here instead of downloading node/npm and running it on your system.

Just use the New File link in the Files list on the left to add new files. To specify a subdirectory, just add the path to the file name when creating a new file. For example: “src/app/products/product-list.component.ts”

You should then be able to follow the this course using Plunker instead.


The AppRoutingModule Does Not Work

Problem: If you created an AppRoutingModule as defined in the “Revisiting AppModule” clip in the “Angular Modules” course module, the routes may stop working.

Solution: Order matters when defining routes. The AppRoutingModule must be *last* in the list of imports, after any feature modules. The details as to why are provided here:


Twitter Bootstrap Does Not Work Properly

Problem: If you add component features to the sample application using Twitter Bootstrap, they may not work properly. For example, if you add the Twitter Bootstrap styles to display a dropdown menu, the menu does not drop down.

Solution: To keep the sample application focused on the basics of Angular 2, I only added the Twitter Bootstrap styles, not its components. To use any of the Twitter Bootstrap components (such as a dropdown menu), you need jQuery and the Bootstrap JavaScript library:

1. Modify the package.json file to include: "jquery": "2.2.3" (or whichever version you require)

2. Use the following command to update the packages: npm update

3. Include the following in index.html:

  <!–  Support Bootstrap Components –>
   <script src="node_modules\jquery\dist\jquery.min.js"></script>
   <script src="node_modules/bootstrap/dist/js/bootstrap.min.js"></script>  

[[As provided by Scott Simpson]]


Something is Wrong and the Code Doesn’t Work

Problem: JavaScript development in general can be difficult, so often something can go wrong.

Solution: Here are some tips for when your code doesn’t work:

  • JavaScript/Angular are CASE SENSITIVE. For example: “*ngIF” and “ngif” won’t work, must be “*ngIf”. This includes names. For example “@Angular/core” won’t work, must be “@angular/core”. If you name a route “products” it must be called “products” everywhere, and not “Products”. If you name your interface “IProduct” it must be called “IProduct” and not “Iproduct”. And so on.
  • Check the developer tools and view the console. Angular errors are shown there. Sometimes a little error causes a large message in the console. Start with the first or second line of the message. That often tells you exactly what is wrong.
  • Watch for typographical errors and syntax errors in the HTML. Unlike most Web apps, Angular is *not* forgiving when it comes to errors in the HTML. A missing or incorrect closing tag could prevent the application from working.
  • Try stopping and restarting the local server with ‘npm start’ again. Sometimes, especially when working with pipes and guards, the local server needs to be restarted for the changes to be fully recognized.
  • Try using a file compare utility and checking your code against the code for the course. You can find the starter files and final files in the github repo for this course. AND you can find the code as it should be at the end of each module using the “Exercise Files” tab on the Pluralsight page for the course.
  • Take care when finding solutions on the internet. Be sure the solution is appropriate for your version of Angular. Angular changed significantly from the Angular 2 RC versions to the final Angular 2 release. So any information posted prior to Angular 2’s release in September of 2016 can lead you down the wrong path.


“Can’t bind to ‘ngModel’ since it isn’t a known property of ‘input’.”

Problem: You will see the above message in the console.

Solution: This normally means that you are missing importing the FormsModule in your AppModule (or feature module).


How Do I Deploy this Application?

Problem: After you build an application, you’ll want to deploy it!

Solution: There are detailed instructions here:

You can also find a module on deployment here:


How Do I Debug Angular?

Problem: Here was the question from a viewer: “Since the ts is compiled to js, there is a disconnect there for tracing code back to the source files…what tools do you recommend?”

Solution: TypeScript creates a map file that maps the js to your ts files. The best way to debug is to use the Chrome browser developer tools. With them you can set break points in your ts code.

See this link for more information:


Can I Do This Course With Visual Studio Instead?

Problem: The demos in this course use VSCode as the editor. Can Visual Studio 2015/2017 be used instead?

Solution: If you are able to get started with Visual Studio 2015 and are comfortable using it for Javascript/typescript development, then you should have no difficulty using it for this course. See these links for more information: and

I have *not* been using vs 2015 for Angular so am not really prepared to help anyone with it. So for anyone with difficulty, I recommend sticking with VS code because the course shows the steps with it.

When I did try using vs 2015 with Angular a while back I had problems getting the browser sync to work so I had to continually stop and restart. I didn’t want beginners with Angular to get frustrated or confused by this.

One viewer said this: “… the issue seems to be that in VS 2015 you need to explicitly rebuild the solution after certain changes, as they are not picked up just by making the change and then re-running the site. I think I might switch over to Visual Studio Code as the dev environment {:O)”

Working with VS 2017 and Angular is expected to be a much better experience with "dotnet new angular":


Can We Use SCSS Instead of CSS?

Problem: If you are using another style sheet tools, you may be wondering how to use them with Angular.

Solution: Here are some suggestions:

– If you use @angular/cli then you can use the info here:

– If you use WebPack (but not the CLI), there is info here: and here:

– If you want to use systemjs (like is used in this course) as is, then you can add a build step to your process that builds the css from the scss and then use the css in the component.

– If you want to use a loader with systemjs and then reference the scss instead of the css in the component, check out this: PLEASE NOTE: See the warning it provides on using this with TypeScript.

I personally have not tried any of these … so I’d be interested to hear what worked for you.


Where Do I Go Next?

Problem: If you’ve finished the course, you may wonder where you should next on your Angular journey.

Solution: Here are some suggestions:

Why Angular? Why Angular 2?

Filed under: Angular,JavaScript @ 10:52 am
Tags: , , ,

Why Angular and not some other JavaScript framework? (And there are lots of JavaScript frameworks out there!)


· Angular makes our HTML more expressive. It powers up our HTML with features such as if conditions, for loops and local variables.

· Angular has powerful data binding. We can easily display fields from our data model, track changes, and process updates from the user.

· Angular promotes modularity by design. Our applications become a set of building blocks, making it easier to create and reuse content.

· And Angular has built-in support for communication with a back-end service. This makes it easy for our Web applications to integrate with a backend service to get and post data or execute server-side business logic.

No wonder Angular is so very popular with Web developers!

With so many developers already using Angular 1, why do we need an Angular 2?


· Angular 2 is built for speed. It has faster initial loads, faster change detection and improved rendering times.

· Angular 2 is modern. It takes advantage of features provided in the latest JavaScript standards and beyond such as classes, modules, and decorators. And it leverages Web Component technologies for building reusable user interface widgets. Yet it supports both green field and legacy browsers: Edge, Chrome, Firefox and Internet Explorer back to IE 9!

· Angular 2 has a simplified API. It has fewer built-in directives to learn, simpler binding, and a lower overall concept count.

· And Angular 2 enhances our productivity to improve our day-to-day workflow by providing a consistent pattern for writing our code.

For more information on Angular 2, check out my “Angular 2: Getting Started” course from Pluralsight.

Angular 2: Getting Started

Filed under: Angular,JavaScript @ 10:43 am
Tags: , , ,

Whether you are new to Angular or new to Angular 2, you’re going to want to come up to speed quickly with Angular 2’s components, templates, and services. My latest Pluralsight course “Angular 2: Getting Started” provides the basics you need to get started building an Angular 2 application.


The course covers the following topics:


o We start with first things first. We’ll select a language and editor to use. Then walk through how to set up an Angular 2 application.

o Next we’ll dive into components. We’ll build the App component using a simple template and minimal component code and metadata. Here the focus is on the code including the what, why, and how.

o We’ll see how to build the user interface for our application using templates, interpolation, and directives.

o We’ll power up that user interface with data binding and nicely format our data with pipes.

o Next we’ll tackle some additional component techniques. We’ll define interfaces, encapsulate styles, and leverage lifecycle hooks to build better components.

o We’ll see how to build a component designed to be nested within other components. And how to communicate between the nested component and its container.

o We often have logic or data that is needed across components. We’ll learn how to build services specifically for this purpose and use dependency injection to inject those services into the components that need them.

o Most Web applications need to communicate with a back-end server to get or post data and to execute back-end business logic. In this module, we’ll leverage http and observables to retrieve the data for our application.

o Our sample application displays multiple views. We’ll see how to set up routing to navigate between those views.

We’re covering a lot of territory. And by the end of our journey, we’ll have a simple, but fully operational Angular 2 application that you can use as a reference for your own development.


February 24, 2016

Understanding C# Delegates

Filed under: C#,LINQ @ 12:10 pm

Delegates are sometimes seen as an ethereal concept, bodiless and hard to grasp. But they don’t have to be that way.

In my latest Pluralsight course: “C# Best Practices: Collections and Generics“, I walk through what a delegate is and how to understand them.


A delegate is simply a type that represents a reference to a method with a specific parameter list and return type. The primary purpose of delegates is to pass methods as arguments to other methods.

Here is an example of a method that needs a delegate:

var filteredList = vendors.Where(???);

In the above line of code, we use the LINQ Where method to filter a list of vendors. The Where method needs a selector defining the logic to be used for the filtering. Do we want to filter the list of vendors by some keyword in their name? Or by how much they currently owe us? Or by the product types that they sell? Somehow we need to specify this logic. We do that with a method.

What does that method need to look like? In Visual Studio, Intellisense shows us the signature of the delegate method that it needs. For the LINQ Where method, it is:

vendors.Where(Func<Vendor, bool> predicate)

Let’s break down what Intellisense is telling us here:

  • The “Func” specifies that the method we create has to return a value. If the method does not require a return value, the Intellisense will instead say “Action”.
  • The first generic parameter (Vendor in this example) is the first parameter to the method we create.
  • If there is a return value, the last generic parameter (bool in this example) defines the return value type.

So looking at the example, we know we need to create a method with a bool return value that takes one parameter of type Vendor.

We can then create a method such as this:

private bool FilterCompanies(Vendor v)
   return v.CompanyName.Contains(“Toy”);

This method takes in a Vendor object and returns a Boolean. Specifically, it returns true if the vendor’s company name contains “Toy”. Otherwise it returns false, thereby specifying how we want the vendor list filtered.

We can then pass this method as a delegate to the Where method:

var filteredList = vendors.Where(FilterCompanies);

The resulting filteredList contains the list of vendors whose company name contains “Toy”.

The problem with this approach is that we end up with little methods all over that simply define these delegates. There is another way. We can use Lambda Expressions. Lambda Expressions are basically a short cut syntax for these little methods.

So instead of this:

var filteredList = vendors.Where(FilterCompanies);

private bool FilterCompanies(Vendor v)
   return v.CompanyName.Contains(“Toy”);

We can simply type this:

var filteredList = vendors.Where(v => v.CompanyName.Contains(“Toy”));

For more information, check out: “C# Best Practices: Collections and Generics” from Pluralsight.


January 28, 2016

C# Best Practices: Collections and Generics

Filed under: C#,Lambda Expressions,LINQ @ 12:27 pm

The next in my series of “Best Practices” courses was published today in the Pluralsight library: “C# Best Practices: Collections and Generics“.

This course starts with the classic collection type: arrays. Then it moves on to generics … that challenging to explain topic that often shows up even in the most basic of beginner courses … because without generics we don’t have a good way to work with collections of things. And most applications require working with collections of things.


We move on to cover generic lists and generic dictionaries. Then we dive deeper into generic collections, looking at the interfaces they implement and how to leverage those interfaces as method parameters and return types.


Lastly, we look at Language Integrated Query (or LINQ) for filtering, shaping, ordering, grouping, aggregating, or locating elements in a collection. Along the way we cover extension methods, delegates, and Lambda expressions.



January 26, 2016

Creating a Filter Pipe in Angular 2

Filed under: Angular @ 4:23 pm
Tags: , , ,

Angular 1.x has filters. Angular 2 has pipes, which fulfill a similar purpose. However, there are some key filters in Angular 1.x, such as the "filter filter", that don’t have an equivalent Angular 2 feature. This post details how to build a filter pipe in Angular 2.

Angular 1.x

In Angular 1.x, we define an input box for a user to enter filter text. We then filter a list of items by that text with one simple clause as shown below:

<div class="row">
    <div class="col-md-2">Filter by:</div>
    <div class="col-md-4"><input type="text" ng-model="listFilter" /></div>

<div class="table-responsive">
    <table class="table">
            <tr ng-repeat="movie in vm.movies | filter : {title:listFilter}">
                <td>{{ movie.title}}</td>
                <td>{{ movie.director }}</td>
                <td>{{ movie.mpaa | uppercase}}</td>

Easy breezy.

Angular 2

Angular 2 provides pipes for this same purpose. But with no "filter" pipe in Angular 2, we have to build our own pipe component.

Converting the above code into Angular 2 results in:

<div class="row">
    <div class="col-md-2">Filter by:</div>
    <div class="col-md-4"><input type="text" #listFilter (keyup)="0" /></div>

<table class="table">
        <tr *ngFor="#movie of movies | movieFilter:listFilter.value" >
             <td>{{ movie.title}}</td>
            <td>{{ movie.director }}</td>
            <td>{{ movie.mpaa | uppercase}}</td>

Hmmm. That does not look that different!

A few things you’ll notice here:

  • The local variable, listFilter, is now prefixed with a hash symbol (#) to explicitly identify it as a local variable.
    • This variable defines an HTML element, so to obtain the value, we need to access listFilter.value.
  • The (keyup)="0" syntax sets up an event listener for the keyup event. There is no event handler needed for this event, so it is just set to "0".
  • The filter clause is defined here as movieFilter and we are filtering on the value of the listFilter variable. So our custom pipe is used just like the built-in pipes.

The key is creating the movieFilter pipe. In Angular 1.x, the "filter filter" was built in. In Angular 2, there are some built-in filters, but not a general list filter. So we need to build our own.

The purpose of a pipe is to take in a value, filter that value, and return the filtered result. In this example, the value we are taking in is a list of movies. We filter the movies to only those with a title containing the user-entered text. And we return the filtered result.

Here is the code for the movieFilter. The description follows.

import {Pipe, PipeTransform} from ‘angular2/core’;

    name: ‘movieFilter’
export class MovieFilterPipe implements PipeTransform {

    transform(value: any, args: string[]): any {

       let filter = args[0].toLocaleLowerCase();
       return filter ? value.filter(movie=> movie.title.toLocaleLowerCase().indexOf(filter) != -1) : value;

1) First we import the Pipe and PipeTransform. This is required to build any pipe.

2) We define a Pipe decorator. This tells Angular that this code is a pipe component. And we give the pipe a name: movieFilter. This is the name used in the HTML as part of a template expression.

3) We create a class that provides the processing for our pipe. We export the class so it can be imported by our movie component. And we implement the PipeTransform interface for our tooling. Note that implementing this interface is optional. With the @Pipe decorator, Angular already expects to find a transform method.

4) The PipeTransform interface requires implementing a transform method. This method has two parameters:

  • value: The value being filtered. In our example, this is the list of movies.
  • args: An optional array of parameters, one for each parameter passed to the pipe. In our example, we are passing listFilter.value.

5) We then define a result array which will contain the movies that match the filter criteria.

6) We create a variable to hold the passed in parameter. We use toLocaleLowerCase() so that the filtering won’t be case sensitive.

7) We check the filter variable. If there is no filter defined, we simply return the original value. No need to iterate the list. Otherwise we use the JavaScript filter function to filter the list and return it.

NOTE: This code could be simplified using regular expressions.

Lastly, we need the component:

import {Component} from ‘angular2/core’;
import {MovieFilterPipe} from ‘../common/movieFilter.pipe’

    selector: ‘mh-movie-list’,
    templateUrl: ‘app/movies/movieListView.html’,
    styleUrls: [‘node_modules/bootstrap/dist/css/bootstrap.css’],
    pipes: [MovieFilterPipe]
export class MovieListComponent {


This is the component associated with the movie list view. The two critical steps for the pipe are:

1) Import the MovieFilterPipe.

2) Identify the pipe using the @Component decorator’s pipes array. This provides the list of all custom pipes available for the template.

For more information on Angular 1.x vs Angular 2, see "Angular 1.x to Angular 2 Quick Reference".

For a sample application, see "Angular: 3 Flavors" which has the same application in Angular 1.x, Angular 1.x with TypeScript, and Angular 2.


January 25, 2016

Angular 1 to Angular 2 Quick Reference

Filed under: Angular,AngularJS @ 5:04 pm
Tags: ,

The post that was here has been edited and re-published here:


January 21, 2016

Dividing a C# Application into Components

Filed under: C# @ 2:52 pm
Tags: , ,

A good architecture divides an application into components:

  • We build UI classes in the UI layer
  • Domain entity classes in the business logic layer
  • Data access classes in the data access layer.
  • And library classes in the common library component.

The content for this blog post was taken from the Pluralsight course entitled “C# Best Practices: Improving on the Basics“. Check out this course for more information.


UI Layer

When we add a form to a UI component, such as a Windows Forms, WPF, or a Web Forms project, Visual Studio automatically creates a form class for us. So our application will have one class for each form. The form class should contain code that:

  • Responds to form events by calling the business logic layer to perform needed processing.
  • Includes error handling for any errors that occur.

There is another type of class that you may find in the UI layer, and that is a V/M or View/Model class. A View/Model manages the data and interaction for a single form or view. A View/Model class is often used in cases where the user interface can bind directly to data defined in the View/Model class, such as with WPF.


Business Logic Layer

When defining classes for the business logic of an application we can start by defining a domain model. A domain model identifies the basic business entities to be managed by the application and how they are related.


For example, if Acme Inc needs a feature to order more product inventory from a vendor, we can define a domain model that includes

  • An order.
  • The product to order. So the order “has a” product.
  • And the vendor from whom the company buys that product. So the product “has a” vendor.

We can use the domain model as a starting point for defining the classes in the business logic component. We’ll need a class to manage each order, a class to manage product information, and a class that manages each approved vendor.

Defining the domain model helps us to consider all of the different bits of logic that the application will require and organize that logic into appropriate classes.

Also in the business logic layer we may want Repository classes. Repository classes are responsible for managing the in memory repository of data for the application. For example, when the user requests display of a specific vendor and the products purchased from that vendor, the Repository classes are responsible for getting that data, tracking the state of that data (for example, whether it has been changed) and saving that data using the data access layer.


Data Access Layer

The classes in the data access layer depend on the data access strategy you are using. If you are using Entity Framework, you may not need any classes in this layer because Entity Framework defines them for you.

Common Library Component

We can determine whether specific functionality goes into a library component by looking at the other components. If the functionality is common across layers (or across applications), then it may be better in a library component. For example, code that provides logging, or sends out email.



When is it appropriate to divide an application into components and define classes such as these? Maybe always? Even if we are developing a prototype, way too often that prototype becomes the basis of our real application.

By breaking the application into a set of components early on in the development cycle we start with a strong foundation that can support the application as it grows and changes over time.


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