How to add a delete callback in entity framework?

Question

Inspired by ruby on rails I want to add a delete callback to entity framework. I've started by overriding SaveChanges() to loop over the tracked entities and create an interface which is called whenever an entity gets deleted.

var changedEntities = ChangeTracker.Entries();
foreach (var changedEntity in changedEntities)
{
    if (changedEntity.Entity is IBeforeDelete && changedEntity.State == EntityState.Deleted)
    {
        IBeforeDelete saveChange = (IBeforeDelete)changedEntity.Entity;
        saveChange.BeforeDelete(this, changedEntity);
    }
}

This works quite well, but I figured one problem and I don't know how to solve that. If an entity gets deleted within the callback, the Changetracker needs to be updated to resprect the newly deleted items. How can I solve that? Or is there another solution? Or do I do it wrong?

Or do I do it wrong? That depends on what you do in saveChange.BeforeDelete. — Gert Arnold
– Gert Arnold, Commented May 4, 2016 at 23:01

Chris Curtis · Accepted Answer · 2016-05-05 01:34:27Z

Good question. If I understand you correctly, your BeforeDelete implementations might delete a different entry that also needs to have BeforeDelete called on it. This could recursively go forever, so the only thing I could think of would be to recursively check the change tracker entries to see if new ones were added after the last batch was processed.

Untested:

public override int SaveChanges()
{
    var processed = new List<DbEntityEntry>();
    var entries = ChangeTracker.Entries();

    do
    {
        foreach (var entry in entries)
        {
            processed.Add(entry);

            if (entry.Entity is IBeforeDelete && entry.State == EntityState.Deleted)
            {
                IBeforeDelete saveChange = (IBeforeDelete)entry.Entity;
                saveChange.BeforeDelete(this, entry);
            }
        }
    } while ((entries = ChangeTracker.Entries().Except(processed)).Any());

    return base.SaveChanges();
}

DukeDidntNukeEm · Accepted Answer · 2016-05-04 22:00:10Z

0

you can filter out uncommited entity changes...

var changedEntities = Context.ChangeTracker
    .Entries<TEntity>()
    .Where(e => e.State != EntityState.Detached)
    .Select(e => e.Entity);

and lock on the rest in your "if" block

lock(changedEntity.Entity){ ... interface code }

answered May 4, 2016 at 22:00

DukeDidntNukeEm

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