Tracking does not work when using context.Update() about entityframework.commontools

[gnaeus]

@thoraj, can you give an example of your scenario? I don't understand what do you mean.

Suppose we have an entity Post with CreatorUserId and CreatedUtc properties.
If we call context.Update(post), the following SQL will be generated during SaveChanges:

UPDATE Posts
SET CreatorUserId = @p0,
    CreatedUtc = @p1
    ...
WHERE Id = @p2;

But we get same SQL if we manually owerwrite post.CreatedUtc = new DateTime(2018, 1, 1);

If we load Post from database, the CreatedUtc property already contains a date. Then context.Update marks all properties as changed. And UPDATE statement doesn't really change it's value.

CreatedUtc and CreatorUserId will be erased in DB only if we have detached entity with empty CreatedUtc and CreatorUserId fields. And then we call context.Update() on it. Is this your scenario?

[thoraj]

Yes, that is my scenario.

I have a modified (detached) entity, and I wish to either create a new if it does not exist, or update if it exists. I'm trying to use EF Core tracking instead of doing manual diffs myself.

The code in question looks like this:

            // check if entity exist
            var existingObservation = await _observationCtx.Observations.SingleOrDefaultAsync(o => o.Id == observation.Observation.ObservationId);
            if (existingObservation is null)
            {
                await _observationCtx.AddAsync(obs);
            }
            else
            {
                // Remove the entity from tracking 
                _observationCtx.Entry(existingObservation).State = EntityState.Detached;

                // Update the entity (note that by default, this will update all columns). 
                _observationCtx.Observations.Update(obs);
            }

	    await _observationCtx.SaveChangesAsync();

Before I Update() using the detached entity (obs) I first have to stop tracking the existing (and attached entity).

Of course the alternative to Update() is to do a manual merge, but I would rather not do that and have EFCore tracking machinery do this instead.

Obviously I am open for suggestions, since the current approach is not working very well.

Perhaps the simplest way/compromise is to manually copy the tracking/audit fields from the existing entity?

[thoraj]

I changed the Update() to this:

                var et =_observationCtx.Observations.Update(obs);
                et.Property(p => p.CreatedUtc).IsModified = false;
                et.Property(p => p.CreatorUserId).IsModified = false;

This will tell EF to not update the properties tracking Creation.

[gnaeus]

You are right. Assigning DateTime.Zero to CreatedUtc and default(TUserId) to CreatorUserId is meaningless. But if we explicitely change CreatedUtc to non-default value, I think we should change it in DB too.

I can add this behaviour in the next release.

[gnaeus]

Fixed in 2.0.2