| I have used two different approaches to creating one-to-one relationships in EOF:
1. Use a "real" one-to-one relationship (A <---> B): Connect A & B by pk to pk as you have done. Consider A to be the "owner" of B. (set "owns destination" on the A ----> B relationship) Use "Cascade Delete" rule on A ---> B relationship. Use "Propagates Primary Key" on A ---> B relationship. <------------ This is the key to making this work. Leave B ---> A relationship as optional, nullify (do not propagate key here).
Advantage: Simple to implement not business logic needed. Disadvantage: EOF will create a row in B for every A.
2. Use a one-to-many relationship (A <--->> B): Connect A & B with a one-to-many relationship. Add business logic to restrict the number of B's for each A to one by removing an existing B and replacing it with a new B.
Advantage: Does not need to create empty B's for every A. Disadvantage: Requires business logic to maintain one B for each A.
On Sep 28, 2006, at 2:04 PM, Chuck Hill wrote:
On Sep 27, 2006, at 4:23 PM, Dev WO wrote:
Hi, I though everything was good with my oneToOne (pk to pk) relationship, but not completely in fact.
So A and B have a relationship joining their pk.
But B can be "alone", which means I can have B object without A object.
Well, that won't work. With a PK to PK relationship, EOF expects that both will always exist. You can sort of work around this by making the optional one a to-many and then adding cover methods like
public A a() { return (toAs().count() > 0) ? return (A)toAs().objectAtIndex(0) : null; }
So it happens that sometimes, when creating a A object (which will create the B object at the same time as the relationship is created) and trying to save it, A got a primary key already used by B which lead to a crash...
Is there a way to get the primary form the B object instead of the A object? (B pks are always good as I cannot have an A object without a B)
Yes, but that still leaves you with EOF thinking that it has a valid reference to an A object when it does not.
Chuck
I've setup my onetoone on both pk and everything is good:)
Thanks a lot:)
I'll wait for tomorrow for the next question;)
Xavier
You really need to set both directions - EOF will not do it for you.
On Sep 26, 2006, at 3:38 PM, Dev WO wrote:
Hi zak, Dev WO wrote on 9/25/06 1:26 PM: So this one is a oneToOne relationship, with is specified in both entities A and B.
[...]
A and B have a foreign key to each other, but only A gets it... B's foreign key stay "null".
I think you may not be modeling the relationship correctly. If you really want a 1-to-1, A and B should share the same primary key and A should be propagating its primary key to B.
If both tables have their own primary keys, and both have foreign keys to each other, things don't really stand up from a relational logic point of view because you actually have two relationships -- A is joined to B by by A.b_id and B is joined to A by B.a_id.
Assuming that A.setB() is defined in terms of A.b_id, the reason B.a_id doesn't update is that B.a() is defined by B.a_id but the relationship you just set is defined by A.b_id. You have two separate relationships based on two separate keys.
HUUUUUU I feel stupid...not the first time though, and probably not the last one too;)
In my case, B can exist alone (without any A to relating to it), but A cannot exist alone, it must be linked to a B.
Does this change anything? I'll try to make the relationship between pks.
Thanks:)
Xavier
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