How to: Use the Entity Framework Code First in XAF

• Feb 24, 2022
• 8 minutes to read

This topic demonstrates how to create a simple XAF application with a business model in a DbContext context.

Note

• This topic demonstrates the code that can be generated automatically by the Solution Wizard. Proceed, if you want to implement the demonstrated functionality in the existing XAF solution. If you are creating a new XAF solution, use the wizard instead.

• A more complex example is provided in the EFDemoCodeFirst application that is shipped with XAF.

Tip

A complete sample project is available in the DevExpress Code Examples database at https://supportcenter.devexpress.com/ticket/details/e4375/how-to-use-the-entity-framework-code-first-in-xaf.

1. Create an XAF Application

Create a new XAF solution called MySolution using the DevExpress v19.2 XAF Solution Wizard. Select Entity Framework Code First at the Choose ORM step and click Finish.

2. Add the Entity Data Model and Context

In this topic, we will not describe entities and context implementation in detail, as it is already described in MSDN (see Code First to a New Database). Here, we assume that you are already familiar with creating an EF data model in code.

• In the module project, implement the following Employee and Task classes.

  Employee (C#)

  using System;
  using System.Collections.Generic;
  using System.ComponentModel;
  using System.Runtime.CompilerServices;
  using DevExpress.Persistent.Base;
  // ...
  [DefaultClassOptions, ImageName("BO_Employee")]
  public class Employee : INotifyPropertyChanged
  {
      private int id;
      [Browsable(false)]
      public int Id { 
          get { return id; }
          protected set {
              if (id != value) {
                  id = value;
                  OnPropertyChanged();
              }
          }
      }
      private string firstName;
      public string FirstName {
          get { return firstName; }
          set {
              if (firstName != value) {
                  firstName = value;
                  OnPropertyChanged();
              }
          }
      }
      private string lastName;
      public string LastName {
          get { return lastName; }
          set {
              if (lastName != value) {
                  lastName = value;
                  OnPropertyChanged();
              }
          }
      }
      private DateTime? birthday;
      public DateTime? Birthday {
          get { return birthday; }
          set {
              if (birthday != value) {
                  birthday = value;
                  OnPropertyChanged();
              }
          }
      }
      private List<Task> tasks;
      public virtual List<Task> Tasks {
          get { return tasks; }
          set {
              if (tasks != value) {
                  tasks = value;
                  OnPropertyChanged();
              }
          }
      }
      #region INotifyPropertyChanged members
      public event PropertyChangedEventHandler PropertyChanged;
      protected void OnPropertyChanged([CallerMemberName] string propertyName = null) {
          PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
      }
      #endregion
  }
  

  Employee (VB.NET)

  Imports System
  Imports System.Collections.Generic
  Imports System.ComponentModel
  Imports System.Runtime.CompilerServices
  Imports DevExpress.Persistent.Base
  ' ...
  <DefaultClassOptions, ImageName("BO_Employee")>
  Public Class Employee
      Implements INotifyPropertyChanged
      Private _id As Integer
      <Browsable(False)>
      Public Property Id() As Integer
          Get
              Return _id
          End Get
          Protected Set(ByVal value As Integer)
              If _id <> value Then
                  _id = value
                  OnPropertyChanged()
              End If
          End Set
      End Property
      Private _firstName As String
      Public Property FirstName() As String
          Get
              Return _firstName
          End Get
          Set(ByVal value As String)
              If _firstName <> value Then
                  _firstName = value
                  OnPropertyChanged()
              End If
          End Set
      End Property
      Private _lastName As String
      Public Property LastName() As String
          Get
              Return _lastName
          End Get
          Set(ByVal value As String)
              If _lastName <> value Then
                  _lastName = value
                  OnPropertyChanged()
              End If
          End Set
      End Property
      Private _birthday? As Date
      Public Property Birthday() As Date?
          Get
              Return _birthday
          End Get
          Set(ByVal value? As Date)
              If Not _birthday.Equals(value) Then
                  _birthday = value
                  OnPropertyChanged()
              End If
          End Set
      End Property
      Private _tasks As List(Of Task)
      Public Overridable Property Tasks() As List(Of Task)
          Get
              Return _tasks
          End Get
          Set(ByVal value As List(Of Task))
              If _tasks IsNot value Then
                  _tasks = value
                  OnPropertyChanged()
              End If
          End Set
      End Property
      #Region "INotifyPropertyChanged members"
      Public Event PropertyChanged As PropertyChangedEventHandler _
      Implements INotifyPropertyChanged.PropertyChanged
      Protected Sub OnPropertyChanged( _
          <CallerMemberName> Optional propertyName As String = Nothing)
          Dim args As New PropertyChangedEventArgs(propertyName)
          RaiseEvent PropertyChanged(Me, args)
      End Sub
      #End Region
  End Class
  

  Task (C#)

  using System.ComponentModel;
  using System.Runtime.CompilerServices;
  using DevExpress.Persistent.Base;
  using DevExpress.ExpressApp.DC;
  // ...
  [DefaultClassOptions, ImageName("BO_Task")]
  public class Task : INotifyPropertyChanged
  {
      private int id;
      [Browsable(false)]
      public int Id { 
          get { return id; }
          protected set {
              if (id != value) {
                  id = value;
                  OnPropertyChanged();
              }
          }
      }
      private string subject;
      public string Subject {
          get { return subject; }
          set {
              if (subject != value) {
                  subject = value;
                  OnPropertyChanged();
              }
          }
      }
      private string description;
      [FieldSize(FieldSizeAttribute.Unlimited)]
      public string Description {
          get { return description; }
          set {
              if (description != value) {
                  description = value;
                  OnPropertyChanged();
              }
          }
      }
      private Employee assignedTo;
      public virtual Employee AssignedTo {
          get { return assignedTo; }
          set {
              if (assignedTo != value) {
                  assignedTo = value;
                  OnPropertyChanged();
              }
          }
      }
      #region INotifyPropertyChanged members
      public event PropertyChangedEventHandler PropertyChanged;
      protected void OnPropertyChanged([CallerMemberName] string propertyName = null) {
          PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
      }
      #endregion
  }
  

  Task (VB.NET)

  Imports System.ComponentModel
  Imports System.Runtime.CompilerServices
  Imports DevExpress.Persistent.Base
  Imports DevExpress.ExpressApp.DC
  ' ...
  <DefaultClassOptions, ImageName("BO_Task")>
  Public Class Task
      Implements INotifyPropertyChanged
      Private _id As Integer
      <Browsable(False)>
      Public Property Id() As Integer
          Get
              Return _id
          End Get
          Protected Set(ByVal value As Integer)
              If _id <> value Then
                  _id = value
                  OnPropertyChanged()
              End If
          End Set
      End Property
      Private _subject As String
      Public Property Subject() As String
          Get
              Return _subject
          End Get
          Set(ByVal value As String)
              If _subject <> value Then
                  _subject = value
                  OnPropertyChanged()
              End If
          End Set
      End Property
      Private _description As String
      <FieldSize(FieldSizeAttribute.Unlimited)>
      Public Property Description() As String
          Get
              Return _description
          End Get
          Set(ByVal value As String)
              If _description <> value Then
                  _description = value
                  OnPropertyChanged()
              End If
          End Set
      End Property
      Private _assignedTo As Employee
      Public Overridable Property AssignedTo() As Employee
          Get
              Return _assignedTo
          End Get
          Set(ByVal value As Employee)
              If _assignedTo IsNot value Then
                  _assignedTo = value
                  OnPropertyChanged()
              End If
          End Set
      End Property
      #Region "INotifyPropertyChanged members"
      Public Event PropertyChanged As PropertyChangedEventHandler _
      Implements INotifyPropertyChanged.PropertyChanged
      Protected Sub OnPropertyChanged( _
          <CallerMemberName> Optional propertyName As String = Nothing)
          Dim args As New PropertyChangedEventArgs(propertyName)
          RaiseEvent PropertyChanged(Me, args)
      End Sub
      #End Region
  End Class
  

  The INotifyPropertyChanged interface allows you to receive notifications from business classes when their property values are changed.

  In this code, you see the use of Data Annotations that influences UI generation - DefaultClassOptionsAttribute, ImageNameAttribute and FieldSizeAttribute, as well as the standard .NET Browsable attribute. As a result, the Employee and Task navigation items will be created, icons from the built-in image library will be used, the multiline editor will be displayed for the Task.Description property, and the service Id properties will be invisible in UI.

  Note

  You can use EF Power Tools to reverse engineer an existing database instead of writing code manually.

• Implement the following DbContext descendant.

  C#

  using System.Data.Entity;
  // ...
  public class MyDbContext : DbContext {
      public MyDbContext(string connectionString) : base(connectionString) { }
      public DbSet<Employee> Employees { get; set; }
      public DbSet<Task> Tasks { get; set; }
  }
  

  VB.NET

  Imports System.Data.Entity
  // ...
  Public Class MyDbContext
      Inherits DbContext
      Public Sub New(ByVal connectionString As String)
          MyBase.New(connectionString)
      End Sub
      Private privateEmployees As DbSet(Of Employee)
      Public Property Employees() As DbSet(Of Employee)
          Get
              Return privateEmployees
          End Get
          Set(ByVal value As DbSet(Of Employee))
              privateEmployees = value
          End Set
      End Property
      Private privateTasks As DbSet(Of Task)
      Public Property Tasks() As DbSet(Of Task)
          Get
              Return privateTasks
          End Get
          Set(ByVal value As DbSet(Of Task))
              privateTasks = value
          End Set
      End Property
  End Class
  

Note that the MyDBContext class should implement a constructor that takes the connectionString string parameter. This constructor will be called by the EFObjectSpaceProvider Object Space Provider internally.

3. Use the Entity Framework Object Space Provider

To use the EFObjectSpace instances to access data in your application, modify the default implementation of the CreateDefaultObjectSpaceProvider method located in WinApplication.cs (WinApplication.vb) and WebApplication.cs (WebApplication.vb) files. For details on this code, refer to the Use the Entity Framework Data Model topic.

C#

using DevExpress.ExpressApp.DC;
using DevExpress.ExpressApp.EF;
// ...
protected override void CreateDefaultObjectSpaceProvider(CreateCustomObjectSpaceProviderEventArgs args) {
    args.ObjectSpaceProvider = new EFObjectSpaceProvider(typeof(MyDbContext), args.ConnectionString);
}

VB.NET

Imports DevExpress.ExpressApp.DC
Imports DevExpress.ExpressApp.EF
' ...
Protected Overrides Sub CreateDefaultObjectSpaceProvider( _
ByVal args As CreateCustomObjectSpaceProviderEventArgs)
    args.ObjectSpaceProvider = New EFObjectSpaceProvider(GetType(MyDbContext), args.ConnectionString)
End Sub

4. Specify the Connection String to the Database

To connect the database that was generated for your data model, specify the XafApplication.ConnectionString property in code or use the corresponding option in the App.config and Web.config files located in the WinForms and ASP.NET application projects. Refer to the Connect an XAF Application to a Database Provider topic for details.

5. Run the Application

Now you can run both the Windows Forms and ASP.NET applications. You will see that a UI is automatically generated for your data model.

Windows Forms:

ASP.NET:

Note

To learn how to fill the database with predefined data, refer to the How to: Supply Initial Data for the Entity Framework Data Model topic.