Re: Strange error message

Hi!

>Sorry, but to me this sounds like a bug: it means you can't have legacy 
>databases which have horizontal inheritance and a common set of PKs - 
>which sounds like a pretty severe restriction to me.
>
>Also, I see no reason why the GlobalID should contain the root entity 
>and not the actual one.

I am jumping into this discussion not knowing what has been said yet.

The main catch is that you might want to have to-one relationships to an entity which has children. E.g. The abstract entity Vehicle has two concrete implementations: Bicycle and Car. A Person object has one Vehicle. In that situation EOF creates a fault for the to-one relationship. That fault is identified by a global ID that references the destination entity of the relationship (Vehicle in the example). Only when the fault is tripped EOF tries to figure out which concrete entity is at the end of that relationship. For that it will query both the Bicycle and Car tables with the primary key found in the fault's globalID. It will use the first matching record. Thus IDs need to be unique. As a side effect, if you already had an EO in the editing context that matched the globalID that one would get used. This could lead to seemingly random errors where depending on what was fetched previously one or the other of the possible concrete instances is used.

In the case of legacy databases you may work around this restrictions if you no for sure that you don't have (and never will have) to-one relationships to the root entity, but only to leaf entities.
In that event you can define the inheritence in your EOModel and have the classes generated appropriately, but then programatically break the inheritence at model load time.

A cleaner solution that implies more work is not to define the inheritence in EOModeler but only in your classes. I.e. you would manually create the common abstract parent class. This approach has the advantage of effectively prebenting offenting relationships to be created.

Caveat: WO 5.1 has made changes to how to-one realtionships to abstract entities are handled. It seems to me that those faults are immediately tripped. I have not looked into this in detail and don't know if or how it influences the above.

Pierre.