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

• Jan 23, 2019
• 6 minutes to read

This tutorial will guide you through the process of creating a code-first Data Access Layer. This layer will later be used by the Scaffolding Wizard to generate an application.

1. In Visual Studio, go to “File | New | Project” or press CTRL+SHIFT+N to create a new project. Select the DevExpress Template Gallery option and choose the “Blank Application” template.

2. Right-click your solution in the VS Solution Explorer window and click “Add | New Folder”. Rename this new folder “Model”.

   

3. Select the newly created folder, then press “SHIFT+ALT+C” to add a new class named “Department”. Repeat the process four times more to add the “Course”, “Employee”, “DepartmentContext” and “DepartmentContextInitializer” classes. The figure below illustrates the result in the VS Solution Explorer window.

   

4. This data set will store entities of the “Department”, “Course” and “Employee” classes in related data tables. Thus, populate each of these classes with the desired properties (data fields).

   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
   

5. The following steps involve using the Entity Framework DbContext, so add the related NuGet package to your project. To do this, go to “Project | Manage NuGet Packages…” in Visual Studio, then search for the “EntityFramework” package and install it.

   

6. Derive your “DepartmentContext” class from DbContext and declare three properties of the System.Data.Entity.DbSet type. This class will represent a Data Access Layer and allow you to query and save data. DbSet properties, in turn, will represent tables that store records of related types.

   C#

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

   VB.NET

   
   Friend 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
   

7. Declare a database initializer. This object will populate your database with sample data as 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(ByVal context As DepartmentContext)
           MyBase.Seed(context)
   
           Dim department1 As Department = New Department With {.Name = "Music"}
           Dim department2 As Department = New Department With {.Name = "Journalism"}
           Dim department3 As Department = New Department With {.Name = "Management"}
           context.Departments.Add(department1)
           context.Departments.Add(department2)
           context.Departments.Add(department3)
   
           context.Courses.AddRange( {
               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 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
   

   Note that in this code sample, your initializer is derived from the System.Data.Entity.DropCreateDatabaseIfModelChanges class. This initializer removes, re-creates and re-populates the database only if the model was changed since the last time the database was created. For this reason, your final application will not reflect any changes made to sample data in code after the first run. Moreover, any modifications made to your database at runtime will persist through subsequent application runs. If you want your application to start with clean sample data each time, derive the initializer from the DropCreateDatabaseAlways class instead.

8. Finally, register your initializer on application start-up.

   C#

   
   static class Program {
       /// <summary>
       /// The main entry point for the application.
       /// </summary>
       [STAThread]
       static void Main() {
           Database.SetInitializer<DepartmentContext>(new DepartmentContextInitializer());
           //...
           Application.Run(new Form1());
       }
   }
   

   VB.NET

   
   Friend NotInheritable Class Program
   
       Private Sub New()
       End Sub
   
       ''' <summary>
       ''' The main entry point for the application.
       ''' </summary>
       <STAThread>
       Shared Sub Main()
           Database.SetInitializer(Of DepartmentContext)(New DepartmentContextInitializer())
           '...
           Application.Run(New Form1())
       End Sub
   End Class
   

What’s Next?

Congratulations, you have created a sample Data Access Layer with code-first Entity Framework! Check out other Data Access Layer tutorials or proceed to generating an application based on this layer.