Okay, let me try to give an example (although a contrived example).
Entity: Part (PK: partNumber)
Entity: PartAttributes (PK: partNumber)
It's a to-one relationship from Part to PartAttributes, but the
part_attributes table doesn't have to have a row for a given part. If this
were a to-many relationship this would result in just an empty
NSArray<PartAttributes>. I want partAttributes() to return null.
In the old days the only way to model this was to have a to-many
relationship with methods that allow the user to access the data in a to-one
way ([[somePart partAttributes] lastObject]). Or you could but an exception
handler in:
- (PartAttributes *)partAttributes {
NS_DURING
[partAttributes self]; //this would catch the exception thrown
NS_HANDLER
[partAttributes release]; //throws away the fault
partAttributes = nil; //sets the ivar to nil
NS_ENDHANDLER
return partAttributes;
}
I was just wondering if this concept of a PK to PK to-one relationship was
possible these days without jumping through hoops. For this example I
probably wouldn't setup the tables this way in RL, but there are situations
where it is valuable and when dealing with legacy table structures you don't
usually have a choice.
-Lon
On Wed, Jan 13, 2010 at 4:49 PM, Chuck Hill <[email protected]>wrote:
> Modelling it as FK to PK seems like the way to go, unless I am
> misunderstanding what you need.
>
>
>
> On Jan 13, 2010, at 3:24 PM, Lon Varscsak wrote:
>
> Yes it is the same PK in both tables but there are no rows in the
>> relationship. This is a pretty common practice and I just hate modeling a
>> to-many and then provide interfaces as a to-one.
>>
>> On Wed, Jan 13, 2010 at 4:14 PM, Travis Britt <[email protected]>
>> wrote:
>> Short answer: no. Is the PK not really a PK? If it is a real PK, how are
>> there rows without it?
>>
>> On Jan 13, 2010, at 5:53 PM, Lon Varscsak wrote:
>> > Is there a way to model an optional to-one relationship from the primary
>> key to a primary key of another object?
>>
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> Chuck Hill Senior Consultant / VP Development
>
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