Allow HTTP delete of sub resources

[chrismckinnel]

At the moment we have to do something like:

PATCH /model/<id> 

"relation": {
    "remove": [
        {
            "parent_id": 1,
            "child_id": 1,
            "__delete__": True
        }
    ]
}

To delete a many to many relation. Perhaps this has changed slightly on the master branch, but I'm still using the latest tagged release.

Wouldn't it make more sense to be able to a simple:

DELETE /model/<id>/relation/<id>

Seems like it would simplify things a bit.

Thoughts?

[jfinkels]

Hmm, it's a possibility. I suppose I could be convinced of this. Let me think about it. I'm happy to hear more opinions.

[jfinkels]

It occurs to me that perhaps the client shouldn't be given access to the __delete__ power; this should be configured in the database as a cascade rule.

[chrismckinnel]

How would you delete the relation then? The cascade would only delete the many to many entry in the DB if it's parent object was deleted, right?

[jfinkels]

Oh, I suppose delete-orphan only makes sense when being used with a one-to-many relation (for example, when I remove a child from a parent [parent.children.remove(child)], delete the child because it as an orphaned object).

My concern is this: what if the client __delete__s a related instance that may still be related to other instances? Would that leave the database in an inconsistent state?

[chrismckinnel]

If the delete cascades and primary/foreign key constraints are set on the DB / in the models correctly it wouldn't be a problem as the child and all it's related entries in the DB would be deleted.

If the delete cascade wasn't set in the models, I think session.commit() attempts to set the primary key values in the DB to NULL.

If the constraints aren't set correctly in the DB, that's when we'd get an inconsistent state with relations pointing to non-existent parent instances.

Removing the ability to use __delete__ would force people to have correct delete cascades and DB constraints, right? Can't be a bad thing?

[jfinkels]

I think that's correct, so __delete__ functionality should be removed. However, it may be superseded by a more robust relationship URL specification as described in #208, if that gets implemented.