ASP.NET MVC Example with Northwind and Entity Framework Published

The Microsoft ASP.NET MVC Framework was released as a CTP as part of the ASP.NET 3.5 Extensions Preview a short time ago.  Since that time the MVC Framework has gotten a lot of attention in blogs and developer-focused web sites.

Brad Abrams, founding member of the CLR and .NET Framework teams at Microsoft, published a good example of how developers can leverage the MVC Framework with some of the new tools from Microsoft.  The example originated from the MVC example Scott Guthrie put together on his blog demonstrating how the MVC Framework, in its initial form, works. Scott's example is documented very well and can be seen in four parts:

• ASP.NET MVC Framework (Part 1)
• ASP.NET MVC Framework (Part 2): URL Routing
• ASP.NET MVC Framework (Part 3): Passing ViewData from Controllers to Views
• ASP.NET MVC Framework (Part 4): Handling Form Edit and Post Scenarios

The MVC Framework gives developers the flexibility to chose both the view and model engines to suite their needs.   In Scott's example he is using LINQ to SQL models but Brad decides to use the Entity Framework instead, using the Northwind database as the the data source.

Developers can choose from many different model providers, for example:

• NHibernate
• LINQ to SQL
• Entity Framework

We should see other model providers in the future as well, possibly:

• SubSonic
• LLBLGen Pro
• LightSpeed
• ..or who knows

Brad's approach to creating the example leads the developer from the start of the project using the ASP.NET MVC Application and Test.  Developers will need to have the following installed:

• VS2008
• ASP.NET 3.5 Extensions
• ADO.NET Entity Framework Tools Dec 07 Preview
• Northwind sample database (Northwind.mdf)

The Tutorial

The tutorial is rather extensive and is worth looking through carefully to get the full benefits of how the MVC Framework functions and ties everything together.  Using MVC is very different than your everyday Web Forms application and will take some getting used to by even seasoned ASP.NET Web Form developers.

Getting Started

Once the ASP.NET 3.5 Extensions are installed there are a few more project types to choose from including ASP.NET MVC Web Application and ASP.NET MVC Web Application and Test.  The ASP.NET Framework is designed to be tested, Brad uses testing.

File/New Project - Select ASP.NET MVC Web Application and Test

This creates a single solution with both a web application project as well as a project we can use for unit testing.   Both are pre-populated with the basic stuff you need to get going.

Creating the Routes

Routing in an MVC Framework is one of the more interesting aspects of the design.  This is where the developer gets to decide how their pages are found by the application.  In the classic ASP.NET application a page such as home.aspx has a very clear way to get to the page, often something like www.mywebsite.com/home.aspx.  Routing gives the developer a lot of flexibility over this.

One of the powerful new features that ASP.NET MVC brings to the table is the ability to customize the URLs that access your application. The URL routing feature explicitly breaks the connection between physical files on disk and the URL that is used to access a given bit of functionality.   This is important for Search Engine Optimization as well as general usability of the website.    For example, rather than access http://localhost/Products/ItemDetails.aspx?item=42 you can now very give a pretty URL such as http://localhost/Products/CodFishOil

This is done by creating a route table in the global.asax file in the MVC Application.   Luckily for us, the defaults included in the template work perfectly this application. 

RouteTable.Routes.Add(new Route
{
    Url = "[controller]/[action]/[id]",
    Defaults = new { action = "Index", id = (string)null },
    RouteHandler = typeof(MvcRouteHandler)
});

This code spells out the format of the URLs we want to use for our site.  In particular, a URL of the format

http://localhost/Products/Details/CodFishOil

would translate to the ProductsController class (notice we add the "Controller" suffix to the class name to make these classes stand out in the object model at design time).  Then the Action is a method on that class called Details and finally the argument to that details method is CodFishOil. 

It is of course possible to have other formats, simply by changing he regular expression in the URL pattern string.

Creating the Model

The model is the heart of most web applications, almost all have some kind of data store behind them.  The MVC Framework gives developers almost unlimited ability to use any data source and the ability to easily interchange between them.

The model represents the data you are going to use in the application.   In our case, this is a pretty good place to start the core of the application. 

In the App_Data direction of the MVCApplication copy the Northwind.mdf file.  Northwind is likely the most common example database we have for SqlServer... You can download it from the official location, or for just the raw file, feel free to grab it from here.

Next, we need to create a LINQ model on top of northwind to make it easier to work with... You can do this with NHibernate, LinqToSql, Entity Framework , or any other .NET OR-Mapping technology.  As long as it results in .NET Object, the ASP.NET MVC framework can work with it.  In this case I am going to use the Entity Framework.

Right click on the Models directory and select add new item

In the dialog select ADO.NET Entity Data Model.

In the wizard, select "Generate from Database" and then go with the default "Northwnd" connection string.

For our demo, we are only going to use the Categories, Products and Suppliers tables, but you could of course extend this demo to include a richer feature set.  But for now, unselect the Views and Stored Procedures and all the tables except those three..

When you click finished, VS will create a set of .NET classes that are custom built for accessing this database and we get a nice designer for visualizing the data relationships.

Notice, that the default names given to these classes still use the plural names from the database, but in our OR-Mapping they represent single instances, so to make the code easier to read, go in and change all the table names to their appropriate singular form: Category, Product and Supplier.   Then Navigation properties on Product needs to be singular as there is only one Category and Suppler for each product.

Next we need to cleanup the namespace so things look pretty in our code... Right click on the design surface then set the properties such that namespace is "NorthwindModels" and the Entity Container name to "NorthWindEntities"

While we are not 100% done with the model, we have gotten the lion's share of it complete.. Let's switch over and look at the controller.

Creating the Controller

The controller is the brains behind our application.  Think of the controller as the air traffic controller at an airport, giving direction to the coming and going of aircraft.  The controller is in charge of taking data in one hand and handing it off to the view in the other.

Right click on the Controller directory and select "Add new Item".  In the dialog find MVC Controller and be sure to give it a name that ends in the Controller suffix.  In our case we are writing the ProductsController. 

OK, we are ready to start working in  ProductsController.cs

The goal of the controller is to prepare the model for the view.    We want to bring as much logical as possible out of the view because it is so hard to test in the view.  So in the controller, we are going to be accessing the Model and getting it all set up so all the view has to do is spit out some data. 

The first thing we need, is access to our database. 

1. Add the right namespaces... Linq and a reference to our OR mapping.

using System.Linq;
using NorthwindModel;

2. Next, we create an instance of the NorthwindEntities container class.  Nearly all of our actions will access this class.

    public class ProductsController : Controller
    {
        NorthwindEntities Northwind = new NorthwindEntities(); 

OK, now we are ready to create our first action.. Listing all the categories.  Remember the job of the controller is to prepare the model for the view..   When defining a new action, I like to start off by putting a comment that reminds me what the URL is that access this functionality. 

The next thing we do is access the Categories table from the model.  I snap the results to a generic collection class (you may have to add a reference to System.Collections.Generic) then we pass the results to the view named "Categories".    This is a very simple example, later we will see more complex logic here. 

//URL: http://localhost/Products/Categories
[ControllerAction]
public void Categories()
{
    List categories = Northwind.Categories.ToList();
    RenderView("Categories", categories);
}

Next step, we need to create the "Categories" view..

Creating the View

The MVC Framework gives the developer almost as much flexibility here as with models.  Developers can choose from an array of view engines and interchange them as well. 

Right click on the Views folder, add new Directory "Products".  This so we can organize all our views cleanly.  The Right click on Views/Products folder and add new item MVC View Content Page.  We are going to leverage the Master Page that comes with the default project to make this look a little more pretty. 

Call it Categories.aspx... It is important that the view name matches the first argument to the RenderView method above.

The default project puts the master page in Views/Shared/Site.Master

In order to get the strongly typed access to the ViewData we are passing in from the controller, we need to tell the View Page, the type to expect.  This is done by opening up the codebehind (Categories.aspx.cs) and changing the derived type from:

    public partial class Categories : ViewPage
    {
    }
to:

public partial class Categories : ViewPage< List > 
{
}

Then you simply write clean, simple, designable HTML.  Notice here I am looping over all the items returned in ViewData and pushing them out as a link.  I use the MVC helper method Html.ActionLink to create the URL for the List action with the appropriate product ID. 

    
Browse Products


    

         <% foreach (var category in ViewData) { %>
            

               <%= Html.ActionLink(category.CategoryName, new { action="List", id=category.CategoryName }) %>            
            

        <% } %>
    

OK, we are finally ready to run it! 

Hit F5, and navigate to the controller action we just wrote on http://localhost:64701/products/Categories

Clicking on any of the links give you an error, because we haven't written the List action yet.. we will do that next. 

As an aside, if like me, you are in the habit of using "View in Browser" on aspx pages you develop, you are likely to see this error.  To reproduce, right click on Categories.aspx and select View in browser. 

You get an error. Why?  Well, remember with the MVC model, all execution goes through the controller, the views themselves are not runnable.   Future tooling will make this better, but in the mean time, use F5 or you can "run in browser" with default.aspx.. just be sure you have built the solution first!

The List Action View

OK, let's now go back and add the List action that we are missing.  What we need to do here is find all the products with a give Category.   First I need to get all the products out of the model, then I need to ensure that the Category references are loaded.  The entity framework offers an explicit loading model by default.  As such you have to explicitly load any tables you need.  And finally we render the view. 

//example URL:http://localhost:64701/products/List/Confections
[ControllerAction]
public void List(string id)
{
    List products = Northwind.GetProductsByCategory(id);

    //prepare the view by explicitly loading the categories  
    products.FindAll(p => p.Category == null).ForEach(p => p.CategoryReference.Load());

    RenderView("ListingByCategory", products);

}

Notice, i am calling a custom method on the NorthwindDataContext class... Personally I like the idea of keeping all the data access logic encapsulated in that class.  So to define this method, Right click on the Model, add new Item, select CodeFile and name it NorthwindDataContext.cs and give it the implementation.

using System;
using System.Collections.Generic;
using System.Linq;

namespace NorthwindModel
{
    public partial class NorthwindEntities
    {

    }
}

Now you can easily add data access methods to this class... such as the GetProductsByCategory() method we use above. 

public List GetProductsByCategory(string category)
{
    return Products.Where(p => p.Category.CategoryName == category).ToList();
}

Next, we need to add the ListingByCategory view... We follow the same steps from above to add a ListingByCategory.aspx page in the Views/Products/ directory. 

This time, we should make the ViewData be of type List

public partial class ListingByCategory : ViewPage< List > 
 {
 }

Next, to implement the view, we simply loop over the view data and spit it out in the right format.

  
<%--Print out the catagory name--%>  
  <% foreach (var product in ViewData) { %>
  <% if (product.Category.CategoryName != null) {  %> 
    
  <%=product.Category.CategoryName  %>
 
    <% break; %>
 <%} //end if %>
 <%}//end foreach %>
        
    

    
        <% foreach (var product in ViewData) { %>
        
            

                 
                
 
                 <%=product.ProductName %> 
                

                Price: <%=String.Format("{0:C2}", product.UnitPrice)%> 
                  
                    (<%= Html.ActionLink("Edit", new { Action="Edit", ID=product.ProductID })%>)
                
           
            

    
        <% } %>
        
    

Once you add the /Content/Images directory from the sample project you get this:

Brad's example is in C# so Julie Lerman chose to create Brad's example her own way using VB.NET and the AdventureWorksLT database and focusing on more efficient Entity Framework queries.  Julie points out some important factors of her implementation over Brad's.

• My EDM is created from AdventureWorksLT.
• The relationship from AW's SalesOrderHeaders to Customer is the same as the relationship from Northwind's Products to Category. Therefore, where he use Products, I use SalesOrderHeaders and  where he uses Categories, I use Customers.
• One of the keys for getting data easily to a view is that we need to send ONE object (and not an anonymous type) to the view. Yet what we really desire in the case of the List of Order (which also has the Customer Name) and the list of details (which also has data from the order and the customer) is an object graph.

Those developers who would rather just download the completed application and not have to go through the process step-by-step can download the working example from Brad's blog.