Delete Objects from the Database

• Sep 14, 2022
• 4 minutes to read

Useful API

IObjectSpace.Delete method

Marks the specified persistent object and its aggregated objects as deleted from a persistent storage.

IObjectSpace.IsObjectToDelete method

Indicates whether the specified object has been deleted but not committed in the transaction currently in progress.

IObjectSpace.GetObjectsToDelete method

Returns a collection of persistent objects that will be deleted when the current transaction is committed, including objects that will be deleted in the parent transaction(s), optionally.

IObjectSpace.CommitChanges method

Saves all the changes made to the persistent objects belonging to the current Object Space to the database.

IObjectSpace.IsDeleting property

Indicates whether the current Object Space is about to delete an object(s).

IObjectSpace.CustomDeleteObjects event

The IObjectSpace.Delete method raises the CustomDeleteObjects event. Handle this event to replace the default persistent object deletion logic with custom logic.

IObjectSpace.ObjectDeleting event

Occurs when the specified objects are about to be deleted.

IObjectSpace.ObjectDeleted event

Occurs after the specified objects have been deleted from the dataset.

In a Controller

1. Create a new View Controller in a Module project (for example, in MySolution.Module).
2. Use the ViewController.ObjectSpace property to access an Object Space for data-aware operations.
3. Use the Object Space’s methods to delete an object.
4. Call the CommitChanges() method to save changes.

The following Controller contains the Action that deletes completed tasks:

File: MySolution.Module\Controllers\TaskViewController.cs(.vb).

C#

using DevExpress.ExpressApp;
using DevExpress.Persistent.BaseImpl;
using DevExpress.ExpressApp.Actions;
using DevExpress.Persistent.Base;
using DevExpress.Data.Filtering;
using DevExpress.Persistent.Base.General;
using System.Collections.Generic;
// ...
public class TaskViewController : ObjectViewController<ListView, Task> {
    public TaskViewController() {
        SimpleAction deleteCompletedTasksAction = 
            new SimpleAction(this, "Delete completed tasks", PredefinedCategory.Edit);
        deleteCompletedTasksAction.Execute += DeleteCompletedTasksAction_Execute;
    }
    private void DeleteCompletedTasksAction_Execute(object sender, SimpleActionExecuteEventArgs e) {
        CriteriaOperator completedTasksCriteria = 
            CriteriaOperator.FromLambda<Task>(t => t.Status == TaskStatus.Completed);
        IList<Task> completedTasks = ObjectSpace.GetObjects<Task>(completedTasksCriteria);
        ObjectSpace.Delete(completedTasks);
        ObjectSpace.CommitChanges();
    }
}

VB.NET

Imports DevExpress.ExpressApp
Imports DevExpress.Persistent.BaseImpl
Imports DevExpress.ExpressApp.Actions
Imports DevExpress.Persistent.Base
Imports DevExpress.Data.Filtering
Imports DevExpress.Persistent.Base.General
Imports System.Collections.Generic
' ...
Public Class TaskViewController
    Inherits ObjectViewController(Of ListView, Task)
    Public Sub New()
        Dim deleteCompletedTasksAction As New SimpleAction(Me, "Delete completed tasks", PredefinedCategory.Edit)
        AddHandler deleteCompletedTasksAction.Execute, AddressOf DeleteCompletedTasksAction_Execute
    End Sub
    Private Sub DeleteCompletedTasksAction_Execute(ByVal sender As Object, ByVal e As SimpleActionExecuteEventArgs)
        Dim completedTasksCriteria As CriteriaOperator =
            CriteriaOperator.FromLambda(Of Task)(Function(t) t.Status = TaskStatus.Completed)
        Dim completedTasks As IList(Of Task) = ObjectSpace.GetObjects(Of Task)(completedTasksCriteria)
        ObjectSpace.Delete(completedTasks)
        ObjectSpace.CommitChanges()
    End Sub
End Class

Execute Custom Logic Instead of Deleting Objects

1. Create a new View Controller in a Module project (for example, in MySolution.Module).
2. In the overridden OnActivated method, subscribe to the CustomDeleteObjects event.
3. In the event handler, implement custom logic and set the CustomDeleteObjectsEventArgs.Handled property to true to prevent execution of default logic.

The Controller below specifies the IsMarkedAsDeleted property of CustomDeleteObjectsEventArgs.Objects instead of removing them:

File: MySolution.Module\Controllers\CustomDeleteObjectController.cs(.vb).

C#

using DevExpress.ExpressApp;
// ...
public class CustomDeleteObjectController : ObjectViewController<DetailView, Employee> {
    protected override void OnActivated() {
        base.OnActivated();
        ObjectSpace.CustomDeleteObjects += ObjectSpace_CustomDeleteObjects;
    }
    private void ObjectSpace_CustomDeleteObjects(object sender, CustomDeleteObjectsEventArgs e) {
        foreach (object deletingObject in e.Objects) {
            Employee employee = ObjectSpace.GetObject(deletingObject) as Employee;
            // IsMarkedAsDeleted is a custom Employee's property
            employee.IsMarkedAsDeleted = true;
        }
        e.Handled = true;
    }
    protected override void OnDeactivated() {
        ObjectSpace.CustomDeleteObjects -= ObjectSpace_CustomDeleteObjects;
        base.OnDeactivated();
    }
}

VB.NET

Imports DevExpress.ExpressApp
' ...
Public Class CustomDeleteObjectController
    Inherits ObjectViewController(Of DetailView, Employee)
    Protected Overrides Sub OnActivated()
        MyBase.OnActivated()
        AddHandler ObjectSpace.CustomDeleteObjects, AddressOf ObjectSpace_CustomDeleteObjects
    End Sub
    Private Sub ObjectSpace_CustomDeleteObjects(ByVal sender As Object, ByVal e As CustomDeleteObjectsEventArgs)
        For Each deletingObject As Object In e.Objects
            Dim employee As Employee = TryCast(ObjectSpace.GetObject(deletingObject), Employee)
            ' IsMarkedAsDeleted is a custom Employee's property
            employee.IsMarkedAsDeleted = True
        Next deletingObject
        e.Handled = True
    End Sub
    Protected Overrides Sub OnDeactivated()
        RemoveHandler ObjectSpace.CustomDeleteObjects, AddressOf ObjectSpace_CustomDeleteObjects
        MyBase.OnDeactivated()
    End Sub
End Class

Note

• This event is raised only when you use IObjectSpace‘s methods to delete objects.
• XPO has similar functionality out-of-the-box: Deferred and Immediate Object Deletion.

In an XPO Business Class

In XPO business class, you can perform additional business logic in the overridden XPBaseObject.OnDeleting method. The following code snippet demonstrates this. When you have a one-to-many association between two XPO business classes and delete an object of the one side of the association, the reference property of an object of the many side still contains the deleted object key. You can set this reference property value to null (Nothing in VB) as demonstrated below.

C#

using DevExpress.Persistent.BaseImpl;
// ...
public class Employee : Person {
    // ...
    protected override void OnDeleting() {
        base.OnDeleting();
        foreach (object obj in Session.CollectReferencingObjects(this)) {
            if (Session.GetClassInfo(obj).ClassType == typeof(DemoTask)) {
                ((DemoTask)obj).Notes += 
                string.Format("The assigned employee was removed: {0}.\r\n", FullName);
            }
        }
    }
}

VB.NET

Imports Microsoft.VisualBasic
Imports DevExpress.Persistent.BaseImpl
' ...
Public Class Employee
    Inherits Person
    ' ...
    Protected Overrides Sub OnDeleting()
        MyBase.OnDeleting()
        For Each obj As Object In Session.CollectReferencingObjects(Me)
            If Session.GetClassInfo(obj).ClassType Is GetType(DemoTask) Then
                DirectCast(obj, DemoTask).Notes += String.Format("The assigned employee was removed: {0}." & vbCrLf, FullName)
            End If
        Next obj
    End Sub
End Class