How To: Generate Data Access Layer with Entity Framework Code First

• Aug 21, 2023
• 6 minutes to read

This topic gives a step-by-step description of how to generate the Data Access Layer based on a predefined data model with the Entity Framework.

Create an empty WPF application (you can use the Template Gallery to do this), or open an existing project and follow the steps below.

• Define Data Structure
• Add NuGet Package
• Define a Database Context
• Add Sample Data
• What is Next?

Define Data Structure

Create a new file (for example, Model.cs(vb)) and add the following data classes to it.

C#

public class Department {
    public Department() {
        Courses = new HashSet<Course>();
    }
    public int DepartmentID { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Course> Courses { get; set; }
}
public class Course {
    public int CourseID { get; set; }
    public string Title { get; set; }
    public int DepartmentID { get; set; }
    public virtual Department Department { get; set; }
}
public class Employee {
    public int EmployeeID { get; set; }
    public string Name { get; set; }
    public int DepartmentID { get; set; }
    public virtual Department Department { get; set; }
}

VB.NET

Public Class Department
    Public Sub New()
        Courses = New HashSet(Of Course)()
    End Sub
    Public Property DepartmentID() As Integer
    Public Property Name() As String
    Public Overridable Property Courses() As ICollection(Of Course)
End Class
Public Class Course
    Public Property CourseID() As Integer
    Public Property Title() As String
    Public Property DepartmentID() As Integer
    Public Overridable Property Department() As Department
End Class
Public Class Employee
    Public Property EmployeeID() As Integer
    Public Property Name() As String
    Public Property DepartmentID() As Integer
    Public Overridable Property Department() As Department
End Class

Add NuGet Package

Add the Entity Framework NuGet package to your project. Right-click the project in the Solution Explorer and select the Manage NuGet Packages option.

Note

If you do not have the Manage NuGet Packages option, install the latest version of NuGet.

Input the Entity Framework text to the search box, find the EntityFramework package, click Install and accept the License Agreement.

Define a Database Context

Define a database context that represents a session with the database and allows you to query and save data.

C#

public class DepartmentContext : DbContext {
    public DbSet<Department> Departments { get; set; }
    public DbSet<Course> Courses { get; set; }
    public DbSet<Employee> Employees { get; set; }
}

VB.NET

Public Class DepartmentContext
    Inherits DbContext
    Public Property Departments() As DbSet(Of Department)
    Public Property Courses() As DbSet(Of Course)
    Public Property Employees() As DbSet(Of Employee)
End Class

The defined data context represents the Data Access layer in our application.

Add Sample Data

Add the DepartmentContext initializer that will seed the database with sample data when the application starts for the first time.

C#

public class DepartmentContextInitializer : DropCreateDatabaseIfModelChanges<DepartmentContext> {
    protected override void Seed(DepartmentContext context) {
        base.Seed(context);

        Department department1 = new Department { Name = "Music" };
        Department department2 = new Department { Name = "Journalism" };
        Department department3 = new Department { Name = "Management" };
        context.Departments.Add(department1);
        context.Departments.Add(department2);
        context.Departments.Add(department3);

        context.Courses.AddRange(new[] {
            new Course { Title = "First", Department = department1 },
            new Course { Title = "Second", Department = department1 },
            new Course { Title = "Third", Department = department1 },

            new Course { Title = "First", Department = department2 },
            new Course { Title = "Second", Department = department2 },
            new Course { Title = "Third", Department = department2 },

            new Course { Title = "First", Department = department3 },
            new Course { Title = "Second", Department = department3 },
            new Course { Title = "Third", Department = department3 },
        });

        context.Employees.AddRange(new[] {
            new Employee { Name = "Frankie West PhD", Department = department1 },
            new Employee { Name = "Jett Mitchell", Department = department1 },
            new Employee { Name = "Garrick Stiedemann DVM", Department = department1 },
            new Employee { Name = "Hettie Runte", Department = department1 },
            new Employee { Name = "Gabe Flatley", Department = department2 },
            new Employee { Name = "Zetta Beatty", Department = department2 },
            new Employee { Name = "Ms. Luis Jewess", Department = department2 },
            new Employee { Name = "Jefferey Legros III", Department = department3 },
            new Employee { Name = "Margaretta Roberts", Department = department3 },
        });

        context.SaveChanges();
    }
}

VB.NET

Public Class DepartmentContextInitializer
    Inherits DropCreateDatabaseIfModelChanges(Of DepartmentContext)
    Protected Overrides Sub Seed(context As DepartmentContext)
        MyBase.Seed(context)
        Dim department1 As New Department() With {.Name = "Music"}
        Dim department2 As New Department() With {.Name = "Journalism"}
        Dim department3 As New Department() With {.Name = "Management"}
        context.Departments.Add(department1)
        context.Departments.Add(department2)
        context.Departments.Add(department3)

        context.Courses.AddRange(New Course() {
                                 New Course() With {.Title = "First", .Department = department1},
                                 New Course() With {.Title = "Second", .Department = department1},
                                 New Course() With {.Title = "Third", .Department = department1},
                                 New Course() With {.Title = "First", .Department = department2},
                                 New Course() With {.Title = "Second", .Department = department2},
                                 New Course() With {.Title = "Third", .Department = department2},
                                 New Course() With {.Title = "First", .Department = department3},
                                 New Course() With {.Title = "Second", .Department = department3},
                                 New Course() With {.Title = "Third", .Department = department3}})
        context.Employees.AddRange(New Employee() {
                                   New Employee() With {.Name = "Frankie West PhD", .Department = department1},
                                   New Employee() With {.Name = "Jett Mitchell", .Department = department1},
                                   New Employee() With {.Name = "Garrick Stiedemann DVM", .Department = department1},
                                   New Employee() With {.Name = "Hettie Runte", .Department = department1},
                                   New Employee() With {.Name = "Gabe Flatley", .Department = department2},
                                   New Employee() With {.Name = "Zetta Beatty", .Department = department2},
                                   New Employee() With {.Name = "Ms. Luis Jewess", .Department = department2},
                                   New Employee() With {.Name = "Jefferey Legros III", .Department = department3},
                                   New Employee() With {.Name = "Margaretta Roberts", .Department = department3}})
        context.SaveChanges()
    End Sub
End Class

Then, register it on the application startup callback.

C#

public partial class App : Application {
    protected override void OnStartup(StartupEventArgs e) {
        Database.SetInitializer<DepartmentContext>(new DepartmentContextInitializer());
        base.OnStartup(e);
    }
}

VB.NET

Class Application
    Protected Overrides Sub OnStartup(e As StartupEventArgs)
        Database.SetInitializer(Of DepartmentContext)(New DepartmentContextInitializer())
        MyBase.OnStartup(e)
    End Sub
End Class

What is Next?

When, the Data Access Layer is generated, you can use our Scaffolding Wizard to generate the other parts of a database-oriented application. The UI Generation topic describes how to do this step-by-step.