How to customizely handle object deletion in XAF Web Blazor application using Entity Framework?

Hi Herman,

I can delete now the file from the cloud storage that makes me happy, but the part of the file (the metadata) stored in local database is not deleted. The CommitChanges() I call in the method ObjectSpace_CustomDeleteObjects below does not work. I don't understand why. What's I have done wrong?

Code
public class AngleImageDeletionController : ObjectViewController<DetailView, Angle>
    {
        protected override void OnActivated()
        {
            base.OnActivated();
            ObjectSpace.CustomDeleteObjects += ObjectSpace_CustomDeleteObjects;
        }

        private void ObjectSpace_CustomDeleteObjects(object? sender, CustomDeleteObjectsEventArgs e)
        {
            IList<Image> images = ViewCurrentObject.Images;

            foreach (object deletingObject in e.Objects)
            {
                if (deletingObject is Image image && images.Contains(image))
                {
                    image.FileData.DeleteFile();
                    ObjectSpace.Delete(image.FileData);
                }
            }
            e.Handled = true;
            ObjectSpace.CommitChanges();   ===> **The deletion is not persisted**
        }

        protected override void OnDeactivated()
        {
            ObjectSpace.CustomDeleteObjects -= ObjectSpace_CustomDeleteObjects;
            base.OnDeactivated();
        }
    }

there are other ways to handle this usage scenario in XAF. Please refer to the following help topic for more information: Delete Objects from the Database.

You can still override the OnSaving method but process the GetObjectsToSave(Boolean). Alternatively, use GetObjectsToSave(Boolean) and check IObjectSpace.IsObjectToDelete. That is why, we do not offer a separate OnDeleting method in IXafEntityObject.

Of course, you can also use Controllers and handle the IObjectSpace.ObjectDeleting or Committing event. If you handle CustomDeleteObjects, do not call ObjectSpace.Delete and ObjectSpace.CommitChanges - it is architecturally incorrect because CustomDeleteObjects requires you to implement custom logic (for example, through direct SQL). Your current code isn't correct either because it may cause recursion from Delete and CommitChanges methods. In general, I believe CustomDeleteObjects is inappropriate for your task, and it's better to use OnSaving or Controllers, as I noted above.

Hello Dennis,

Thanks for your comments, but I'm not able to follow your suggestions as I don't quite understand it.

Let me try to explain a bit more what I want to achieve.

I have 2 classes, i.e.: Angle and Image Classes.

The Angle Class is:

Code
public class Angle : BaseObject
{
    [RuleRequiredField(DefaultContexts.Save)]
    public virtual required AngleType AngleType { get; set; }

    [Aggregated]
    public virtual IList<Element> Elements { get; set; } = new ObservableCollection<Element>();

    [Aggregated]
    public virtual IList<Image> Images { get; set; } = new ObservableCollection<Image>();
}

Within this Class there is a collection of Images. The Image Class looks as follows:

Code
public class Image : BaseObject
{
    public virtual required FileDataReference FileData { get; set; }

    public virtual required Angle Angle { get; set; }

    [DataSourceProperty("Angle.Elements")]
    public virtual Element? Element { get; set; }

    public string ElementName => Element?.ElementType?.Name ?? string.Empty;
}

Within this Image Class there is a property FileData. Some property of FileData (binary) is stored in the cloud, while some other properties (the metadata) are stored in the local database.

Your colleague, Herman, has helped me to delete the part which is stored in the cloud. But I'm still not successful in deleting those stored in local database.

In the DetailView of Angle Class, you'll get an Images tab shown, along with Elements tab. Within this Images tab you get the list of all Images belonging to this Angle Class (see attachment). On the ListView you have also the standard XAF Actions such as: New and Delete Actions.

My question is, how can I delete the metadata of the FileData of the selected Image(s), as the solution proposed by Herman above only resolves my cloud storage part? Can you explain and/or give me an example how to override the handler of Delete Action of the Images ListView? Also how can I identify which items have been checked for deletion? I think by overriding this handler I can put some codes to delete the metadata part of the FileData from my local database.

I hope I have clearly explained what I want to achieve and that you could give me a workable ideas or solution.

Looking forward to your response,
Kind regards,
Herman.