Entity Framework - CodeFirst Model

Entity Framework

Entity Framework supported the development of applications using Schema first and Model First approach. Now, the new Entity Framework introduced the Code First approach. In Code First approach, we are creating the code first and the Entity framework will automatically generate the corresponding tables. Let us discuss more about Code First approach of Entity Framework here.

NuGet

NuGet is a Visual Studio extension that makes it easy to install and update open source libraries and tools in Visual Studio. We will use NuGet to get the Entity Framework installed. The advantage here is that the associated assemblies will be added to the project automatically.

You can install the NuGet either from http://www.nuget.org/ or using the Extension Manager in Visual Studio 2010 IDE.

Install Entity Framework

After installing NuGet, create your application. Right click on the References and choose Add Library Package Reference option.

 

Select Online and Search for EntityFramework. Select Install to install the Entity Framework.

This will add the assemblies required by the Entity Framework to your application.

Create the Classes

Now Let us create the classes required for our project. For our sample, I am using two classes Student and Marks. Each student will have a list of Marks associated with it.

public class Student
    {
        public int Id { get; set; }
        public string FirstName { get; set;} 
        public string LastName { get; set;}

        public List<Mark> Marks { get; set; }
    }

public class Mark
    {
        public int Id { get; set; }
        public string Subject{ get; set; }
        public int mark { get; set; }
    }

DbContext

CodeFirst depends mainly on the DbContext. DBContext automatically generate the database using the tables defined. We will define our DbContext as

public class MyDbContext: DbContext
    {
        public DbSet<Student> Students { get;set; }
        public DbSet<Mark> Marks { get;set; }

    }

Define Data Access Methods

Now let us define a class with data querying methods. For our sample, we use the StudentData class with a GetStudents method to retrieve the data from the DbContext.

   

public class StudentData
    {
        MyDbContext context = new MyDbContext();

        public List<Student> GetStudents()
        {
            return (from s in context.Students
               select s).ToList();
        }
    }

Define Connection String

Now we need to define the connection string to connect to the database. DbContext will use this connection string to generate the Database and associated tables from the code.

<connectionStrings>
  
   	<add name="MyDbContext"
        connectionString="datasource=.;Integrated Security=SSPI; database=Students"
        providerName="System.Data.SqlClient" />
 
</connectionStrings>

Normally, we will specify the connection string name as DbContext name; but we can use a different name too.

Define the UI

Build the solution. Building the solution is important; otherwise when we try to define a datasource pointing to the Object, our StudentData object will not be available.

Now, let us define the UI to display the data. For our sample, I am having one GridView with a DataSource associated with it. Configure the datasource using our StudentData, which return the Student data as a list.

Select the StudentData defined in the project.

Now, select method used to return the student details.

Run the application

You can observe a blank page. Now, DbContext created the database and tables in the specified server. Let us open the server explorer and verify the same.

You can observe that, there is a new database with name Students is created in the server. You can observe the two tables created under the table – Students & Marks.

You can notice the foreign key generated as part of the Marks table. Also the id fields are generated as identity fields.

There is another table generated with the name EdmMetaData, which will be for tracking the changes. We will discuss about it in latter.

Let us enter some data to the Students table.

Now we will run our application again.

Conclusion

In this article we discussed about the new model of Entity Framework – CodeFirst. We will look more on the Entity Framework and its capabilities latter.

Update

Please find the Solution structure used for constructing the sample Code First project.