IXafEntityObject Interface

Declares methods that are called automatically when a business object is being created, loaded and saved.

Namespace: DevExpress.ExpressApp

Assembly: DevExpress.ExpressApp.v19.1.dll

Declaration

C#

public interface IXafEntityObject

VB.NET

Public Interface IXafEntityObject

Remarks

When a business object supports IXafEntityObject, the Object Space automatically calls the IXafEntityObject.OnCreated, IXafEntityObject.OnLoaded and IXafEntityObject.OnSaving methods of this interface when an object is being created, loaded and saved. Thus, you can implement these methods and add certain business logic directly in the business object code, without the use of Controllers. In most cases, you will need to access other business objects from your code. So you can also implement the IObjectSpaceLink interface to access an IObjectSpace instance and use its methods to query objects.

Note

• The IXafEntityObject interface is intended for use with Entity Framework. With XPO, using the BaseObject.AfterConstruction and BaseObject.OnSaving methods is recommended.

• You can use the XAF Business Object | EF Business Object from Template Gallery to add a class that supports both IXafEntityObject and IObjectSpaceLink.

In the example below, the CreatedBy property refers to a user who created the current object, the LastModifiedBy property refers to a user who last changed the object, and the IsNew property indicates if an object is only created, but not saved (you can use this flag in Conditional Appearance and Validation rules).

C#

using System.ComponentModel;
using System.ComponentModel.DataAnnotations.Schema;
using DevExpress.ExpressApp;
using DevExpress.Persistent.Base;
using DevExpress.Persistent.BaseImpl.EF.PermissionPolicy;
// ...
[DefaultClassOptions]
public class MyEntityObject : IXafEntityObject, IObjectSpaceLink {
    [Browsable(false)]
    public Int32 ID { get; protected set; }
    public string Name { get; set; }
    [NotMapped]
    public bool IsNew { get; protected set; }
    public virtual PermissionPolicyUser CreatedBy { get; protected set; }
    public virtual PermissionPolicyUser LastModifiedBy { get; protected set; }
    PermissionPolicyUser GetCurrentUser() {
        return objectSpace.GetObjectByKey<PermissionPolicyUser>(SecuritySystem.CurrentUserId);
    }
    #region IXafEntityObject members
    void IXafEntityObject.OnCreated() {
        CreatedBy = GetCurrentUser();
        IsNew = true;
    }
    void IXafEntityObject.OnLoaded() {
        IsNew = false;
    }
    void IXafEntityObject.OnSaving() {
        if (objectSpace != null) {
            LastModifiedBy = GetCurrentUser();
        }
        IsNew = false;
    }
    #endregion
    #region IObjectSpaceLink members
    private IObjectSpace objectSpace;
    IObjectSpace IObjectSpaceLink.ObjectSpace {
        get { return objectSpace; }
        set { objectSpace = value; }
    }
    #endregion
}

VB.NET

Imports System.ComponentModel
Imports System.ComponentModel.DataAnnotations.Schema
Imports DevExpress.ExpressApp
Imports DevExpress.Persistent.Base
Imports DevExpress.Persistent.BaseImpl.EF.PermissionPolicy
' ...
<DefaultClassOptions> _
Public Class MyEntityObject
    Implements IXafEntityObject, IObjectSpaceLink
    Private privateID As Int32
    <Browsable(False)> _
    Public Property ID() As Int32
        Get
            Return privateID
        End Get
        Protected Set(ByVal value As Int32)
            privateID = value
        End Set
    End Property
    Public Property Name() As String
    Private privateIsNew As Boolean
    <NotMapped> _
    Public Property IsNew() As Boolean
        Get
            Return privateIsNew
        End Get
        Protected Set(ByVal value As Boolean)
            privateIsNew = value
        End Set
    End Property
    Private privateCreatedBy As PermissionPolicyUser
    Public Overridable Property CreatedBy() As PermissionPolicyUser
        Get
            Return privateCreatedBy
        End Get
        Protected Set(ByVal value As PermissionPolicyUser)
            privateCreatedBy = value
        End Set
    End Property
    Private privateLastModifiedBy As PermissionPolicyUser
    Public Overridable Property LastModifiedBy() As PermissionPolicyUser
        Get
            Return privateLastModifiedBy
        End Get
        Protected Set(ByVal value As PermissionPolicyUser)
            privateLastModifiedBy = value
        End Set
    End Property
    Private Function GetCurrentUser() As PermissionPolicyUser
        Return _objectSpace.GetObjectByKey(Of PermissionPolicyUser)(SecuritySystem.CurrentUserId)
    End Function
    #Region "IXafEntityObject members"
    Private Sub IXafEntityObject_OnCreated() Implements IXafEntityObject.OnCreated
        CreatedBy = GetCurrentUser()
        IsNew = True
    End Sub
    Private Sub IXafEntityObject_OnLoaded() Implements IXafEntityObject.OnLoaded
        IsNew = False
    End Sub
    Private Sub IXafEntityObject_OnSaving() Implements IXafEntityObject.OnSaving
        If _objectSpace IsNot Nothing Then
            LastModifiedBy = GetCurrentUser()
        End If
        IsNew = False
    End Sub
    #End Region
    #Region "IObjectSpaceLink members"
    Private _objectSpace As IObjectSpace
    Private Property IObjectSpaceLink_ObjectSpace() As IObjectSpace Implements IObjectSpaceLink.ObjectSpace
        Get
            Return _objectSpace
        End Get
        Set(ByVal value As IObjectSpace)
            _objectSpace = value
        End Set
    End Property
    #End Region
End Class

Note that it is required to check if an Object Space is null (Nothing in VB) in the OnSaving method. The reason is that the OnSaving method is also called when the current business object is being deleted and the link to the Object Space is already cleared at that moment to avoid memory leaks. If you want to access the Object Space on object deletion, change the IObjectSpaceLink.ObjectSpace property implementation to maintain the Object Space reference.

C#

private IObjectSpace objectSpace;
IObjectSpace IObjectSpaceLink.ObjectSpace {
    get { return objectSpace; }
    set { if (value != null) objectSpace = value; }
}

VB.NET

Private _objectSpace As IObjectSpace
Private Property IObjectSpaceLink_ObjectSpace() As IObjectSpace Implements IObjectSpaceLink.ObjectSpace
    Get
        Return _objectSpace
    End Get
    Set(ByVal value As IObjectSpace)
        If value IsNot Nothing Then
            _objectSpace = value
        End If
    End Set
End Property

In this instance, you should manually set the Object Space to null (Nothing in VB) on deletion. Use the IObjectSpace.IsObjectToDelete method to distinguish whether an object is being saved or deleted:

C#

void IXafEntityObject.OnSaving() {
    PermissionPolicyUser currentUser = objectSpace.GetObjectByKey<PermissionPolicyUser>(SecuritySystem.CurrentUserId);
    if (objectSpace.IsObjectToDelete(this)) {
        // Executed on deletion:
        Tracing.Tracer.LogWarning("The '{0}' user is deleting the '{1}' object", currentUser.UserName, Name);
        objectSpace = null; 
    }
    else {
        // Executed on saving:
        LastModifiedBy = currentUser;
    }
}

VB.NET

Private Sub IXafEntityObject_OnSaving() Implements IXafEntityObject.OnSaving
    Dim currentUser As PermissionPolicyUser = objectSpace.GetObjectByKey(Of PermissionPolicyUser)(SecuritySystem.CurrentUserId)
    If objectSpace.IsObjectToDelete(Me) Then
        ' Executed on deletion:
        Tracing.Tracer.LogWarning("The '{0}' user is deleting the '{1}' object", currentUser.UserName, Name)
        objectSpace = Nothing
    Else
        ' Executed on saving:
        LastModifiedBy = currentUser
    End If
End Sub