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Building a simple ASP.Net application using the Entity Data Model

This is going to be the first post of a series of posts regarding ASP.Net and Entity Framework and how we can use Entity Framework to access(select,insert,update,delete) the database. We will start with some simple samples but then we will look into more advanced uses of Entity Framework.

In order to follow along you must have some knowledge of C# and know what an ORM system is and what kind of problems Entity Framework addresses.It will be handy to know how to work inside the Visual Studio 2010 IDE.

I have a post regarding ASP.Net and EntityDataSource. You can read it here.I have 3 more posts on Profiling Entity Framework applications. You can have a look at them here,here and here.

I will be using Entity Framework version 4.0 that ships with Visual Studio 2010 and .Net 4.0. 

In this very first post we will create a simple website and use Entity Framework as our data access layer.

I assume that you have access to a version of SQL Server and AdventureWorkLT database.

If you do not, you can download and install the free SQL Server Express edition from here. If you need the installation scripts for the sample AdventureWorkLT database, click here

1) Launch Visual Studio 2010 (express edition will work fine). Create a new empty website and choose a suitable name for it. Choose C# as the development language.

2) Add a new item to your site, a web form. Leave the default name, Default.aspx

3) Add a new project to your solution, a class library project.Remove the class1.cs file from the project.

4) Add a new item to your class library project, a ADO.Net Entity Data model. Choose a suitable name for it, e.g AdventureWorkLT.edmx.

5) Then the Wizard pops up. Choose "Generate from Database". Have a look at the picture below

 

 6) Click Next and Create a New Connection (as you see in the picture below) and hit the Continue button.

 

 

7) Then follow the instructions as shown in the picture below.Select the local installation of your SQL Server and the database name and then click OK.

 

 

8) After you complete the steps above you will see something like the picture below. You can see the Entity connection string and where these setting will be saved.Hit the Next button.Then click Finish

 

9)  Now the wizard will identify the database objects and let us choose which database objects we want to include in our model.I included all the database objects.Hit the Finish button.

 

10) Have a look at your entity model as it is visualized in the Entity Model Designer. Have a look at the Entity classes and their relationships/associations.Have a look at the properties of each Entity class. Have also a look at the Navigation Properties of each entity class.Basically the entity framework generates classes for all the entities in the designer. You can have a look at the generated code if you want by opening the class file, which in my case is AdvWorks.Designer.cs.

All the entities that are represented as classes in our AdvWorks.Designer.cs file inherit from EntityObject class

Snippet

public partial class Customer : EntityObject
    {

 

Inside each class you fill find the usual class definition.  This is the public property declaration for the Title property. All the properties in the classes in the entire model have getter and setter methods.There are public properties and private fields.Have a look at the snippet below.

Snippet

public global::System.String Title
        {
            get
            {
                return _Title;
            }
            set
            {
                OnTitleChanging(value);
                ReportPropertyChanging("Title");
                _Title = StructuralObject.SetValidValue(valuetrue);
                ReportPropertyChanged("Title");
                OnTitleChanged();
            }
        }

 We can also have partial methods defined inside the AdvWorks.Designer.cs. This is the pair of methods for the Title property.

Snippet

partial void OnTitleChanging(global::System.String value);
partial void OnTitleChanged();

You can create additional class files and implement the business logic for these methods.

There is another very important class in our AdvWorks.Designer.cs file , AdventureWorksLTEntities which inherits from ObjectContext class.

Snippet

public partial class AdventureWorksLTEntities : ObjectContext

The whole model and all the entities on it are represented by the ObjectContext class.This is an object that gives us a way to connect to the database. This is our gateway to the database. It gives us a way to update,insert,delete objects and keeps a change tracking mechanism.

 ObjectContext class is responsible for relationship management.ObjectContext class manages change tracking.ObjectContext class manages things like concurrency,connections and transactions

All these classes were generated automatically from the underlying xml file. If you want to see the xml file just select the .edmx file and choose to open it with an XML Editor.Inside there you can spend some time looking into the Storage model, the Conceptual model and the Mapping of the two previous models (Storage & Conceptual).

 

11) So we have our conceptual model and we can have a look at it in the entity designer. Choose the SalesOrderHeader and choose Mapping Details and you can see the mapping between the database columns and the class properties. You can rename the properties in the Mapping Details window,if you want.This mapping mechanism knows how to bind the objects values back to the database.

12)  Now we are ready to start querying our database. We will issue Linq to Entities query against the conceptual schema.

In this very first query we want to get the customers that their firstname starts with the letter N.

Just above the Page_Load event handling routine type

Snippet

AdventureWorksLTEntities ctx = new AdventureWorksLTEntities();

We need to create an instance of the AdventureWorksLTEntities to get access to our model. This is something that you always must do in EF projects.

In the Page_Load event handling routine type,

Snippet

GetNames();

We will create a simple void method to get the information we want. The code for the GetNames() method follows

 

Snippet

private void GetNames()
    {
        var query = from custname in ctx.Customers
                    where custname.FirstName.StartsWith("N")
                    orderby custname.FirstName descending
                    select custname;



        foreach (var item in query)
        {
            Response.Write(item.FirstName);
            Response.Write("<br/>");
        }
    }

 

If you are not so familiar with Linq queries, have a look at my other posts in this blog regarding LINQ.

13)  Run your application and you will see all the customer names starting with N displayed on the screen.

14) Let's create a new query and bind the resultset to a GridView control. Add a GridView control to the default.aspx page.

In this query we want to get only the customers that have more than one order and the Title equals "Ms"

In the Page_Load event handling routine comment out everything and  type,

Snippet

 var query = from mycust in ctx.Customers
       join sho in ctx.SalesOrderHeaders on mycust.CustomerID 
equals sho.CustomerID
       into myorders
       where (mycust.Title=="Ms." && mycust.SalesOrderHeaders.Count >= 1)
       select new { mycust.FirstName, mycust.LastName,OrdersCount = 
myorders.Count() };

        GridView1.DataSource = query;
        GridView1.DataBind();
 

15)  Run your application and you will see all the customer firstname,lastname and the number of their respective orders displayed on the screen.

 This is a projection query (uses anonymous types in the background) .

16) Now that we know how to get / select data from the entity data model, let's see how we can insert, update, delete data from the entity data model/database.

 

In the Page_Load event handling routine type,

 

GetSpecificCustomer();
 

We need to add the GetSpecificCustomer() method, so we have

 

Snippet

  private void GetSpecificCustomer()
    {
    var query = from mycust in ctx.Customers
          where mycust.CustomerID == 3
          select new {mycust.CustomerID,mycust.FirstName,mycust.LastName};

        GridView1.DataSource = query;
        GridView1.DataBind();

    }

 

Add a new button to the default.aspx page and in the Button1_Click event handling routine type,

Snippet

var query = ctx.Customers.First(mycust => mycust.CustomerID == 3);
        query.FirstName = "Julia";
        query.LastName = "Ormond";
        ctx.SaveChanges();
        GetSpecificCustomer(); 

17)  Run your application and click the button. Make sure the data has changed in the underlying database.

Feel free to open your local instance of SQL Server and see the actual changes in the database. Another thing you can do is to open SQL Server Profiler and have a look at the T-SQL code generated on the fly from the LINQ to Entities engine.

18) Now we can add another query that inserts a new address for a specific customer.

In the Page_Load event handling comment out everything routine and type,

AddCustomerAddess();

We create a new void method that does that looks something like this

Snippet

private void AddCustomerAddess()
    {

        var query = ctx.Customers.First(mycust => mycust.CustomerID == 5);

        query.CustomerAddresses.Add(new CustomerAddress
        {
            CustomerID = 29485,
            AddressID = 1087,
            AddressType = "Shipping",
            rowguid = Guid.NewGuid(),
            ModifiedDate = DateTime.Now.AddDays(-100)


        }
        );
        ctx.SaveChanges();

    }
19)  Run your application and see the new record in the CustomerAddress table for the specific customer.

20) Let's try to delete all orders for a specific customer.

We need to create a new void method.

Snippet

private void DeleteCustomerOrders()
    {
var query = from sho in ctx.SalesOrderHeaders where sho.CustomerID == 29982 
select sho;

        foreach (var item in query)
        {
            ctx.SalesOrderHeaders.DeleteObject(item);
        }
        ctx.SaveChanges();
    }
 

In the Page_Load event handling comment out everything routine and type,

DeleteCustomerOrders();

21)  Run your application and see the records in the SalesOrderHeader table deleted.

Drop me an email if you need the source code.

Hope it helps!!


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