Re: Modeling an optional to-one relationship
Re: Modeling an optional to-one relationship
- Subject: Re: Modeling an optional to-one relationship
- From: Lon Varscsak <email@hidden>
- Date: Wed, 13 Jan 2010 17:01:23 -0700
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@hidden> 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@hidden> 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?
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Webobjects-dev mailing list (
email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to
email@hidden
--
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Webobjects-dev mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden