Re: Bi-directional One-to-one relationship
Re: Bi-directional One-to-one relationship
- Subject: Re: Bi-directional One-to-one relationship
- From: Des Oates <email@hidden>
- Date: Sat, 16 Apr 2005 15:14:03 +0100
OK Sorry for not being clear, Here's an example.
I created 2 new EOs in a fresh EO model. DataEntity, and StateEntity.
In each a put a couple of Attributes and integer primary keys, PKData, and PKState respectively
To create a relationship I first copy PKState attribute, and paste it into DataEntity. I then cntr + drag from StateEntity.PKState to DataEntity.PKState.
By default that creates a One-to-many relationship. It inserts the relationship properties 'stateentity' and 'dataentitys' into DataEntity and StateEntity respectively.
I want to change this so I highlight StateEntity.dataentitys and open my inspector. I change the 'To Many' property to 'To One' in the relationship's inspector.
I also set its optionality to 'Mandatory' and its delete rule to no action.
On the other side of the relation ship (DataEntity.stateentity) I also set the optionality to Mandatory, set the delete rule to 'cascade' and the tick the 'owns destination'
If at this point I want to check the consistency of the model. I go to the Model Menu, and hit the 'Check Consistency' menu. This reports the following problem:
Relationship dataentitys in entity StateEntity is a to-one relationship, but its destination attribute(s) does not match the primary key of the destination entity.
Is this something I can live with? I don't believe so, since later on I get runtime errors when these objects are created relating to null primary keys, OR duplicate primary keys being created. I also get runtime errors if I create 2 independent and opposing unidirectional to-one relationships.
The only way I can get a one-to-one relationship to work is if I delete the relationship on the destination, which in this case would be 'StateEntity.dataentitys'. Then it works but of course its now unidirectional. I.e. I can't navigate to my DataEntity from my StateEntity. I want to be able to navigate to and from either object.
Sorry for being long winded, but that's about as concise as I could make it.
Des
On 16 Apr 2005, at 13:07, Drew Thoeni wrote:
If you are talking about setting up a o-o relationship, then yes EOmodeler will do this. Create the two tables, ctrl-drag from the primary key in one to the PK in the other and in the resulting window, click "to one".
I suspect you are, though, asking a more complex question. If you are, perhaps you can clarify with an example.
Drew
On Apr 16, 2005, at 8:01 AM, Des Oates wrote:
Does anyone know if EO Modeler supports a one-to one relationship where each related object is referenced as a property in the other? I've been trying to set up my EOModel like this for a while now, but no matter which way I try to do it EO Modeler complains.
A use case of this would be if you have a single data object, linked to its corresponding single state object. In O-O you would want to keep the logic handling these separate. (I.e. 2 different classes)
I ended up working around this so its not a showstopper for me but I'm just curious for future reference if anyone's actually managed to do it, and if so how.
thanks
Des
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