Fabrice,
The problem that you are having is related to primary key
generation. There is no way for EOF to guarantee the generation of
the same primary key values to two different entities. This is why
modeling one-to-one relationships in EOF normally uses primary key
propagation. What happens is that EOF would generate a new key for
Entity A, then through propagation would assign that same key to the
primary key of Entity B. The downside to this method is that you
will always have a B for every A. This makes sense when you think
about the object graph. Accessing B through the relationship in A
needs to have a database row available when the fault representing B
gets fired by accessing it.
The simplest solution to this problem is to model your one-to-one
relationship just like a one-to-many relationship. Then add code to
your model classes to ensure that the "many side" of the relationship
can only contain one item.
Entity A
idA
fld1
fld2
...
fldn
Entity B
idB
idA <<---- foreign key to A
fld1
fld2
...
fldn
Entity A <-------------->> Entity B
Constrain the relationship A ------->> B to having only one B by
using a cover method for managing that side of the relationship.
Have the cover method remove any existing B objects before adding the
new B object to the relationship. You can also add a cover method
for reading B objects through A. Have the "getter" cover method
return the first object in the A --------->> B relationship.
This design pattern seems to be fairly typical in Object Relational
Modeling environments that I've seen.
On Jan 11, 2007, at 4:50 AM, Fabrice Pipart wrote:
Hi all !
I recently modeled my first one-to-one relationship in my EOModel
(please dont laugh).
And of course I had troubles ;-)
I want this relationship to be optional and to be both sided.
Here is how I did it :
Entity A
idA
bFid
bRelationship (source bFid, destination idB)
Entity B
idB
aFid
aRelationship (source aFid, destination idA)
I want both relationships to be optional.
There is no propagate primary key since I don't really understand
how it works.
The problem is :
if I set A in B, I do have aFid set in DB but I don't have bFid
set :-(
I tried to understand the mechanisms of optional one-to-one
relationships in the mailing list archives but I could not figure
it out.
Could someone please summarize what is a good way to model it?
Regards
Fabrice
www.easyshadow.com
International Corporate Consulting
Palais de la Scala
1 avenue Henri Dunant
Suite 1155
MC - 98000 Monaco
Skype: fabrice.pipart
Tel. +377 97 98 21 04 (direct)
Fax. +377 97 70 88 07
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