NSPredicate complex groups
NSPredicate complex groups
- Subject: NSPredicate complex groups
- From: Arved von Brasch <email@hidden>
- Date: Wed, 31 May 2006 01:33:14 +1000
Greetings Cocoa Dev List,
I have three CoreData Entities in relationships. The relationship is
named 'keywords' on one side and 'articles' on the other. The
keyword entity has an attribute 'name'. Articles are in a standard
parent - children relationship with themselves for use in a
NSTreeController. I have a list of article groups, and want to find
out if any of each groups children has a keyword with a particular name.
To illustrate:
ArticleGroup <-parent--children--> Article <<-articles--keywords->>
Keyword
I know the keyword name I'm searching for, and have a list of
ArticleGroups, how can I construct a Predicate to filter the
ArticleGroups to only include those groups that have Articles with
the keyword name of interest?
I have tried the obvious: ANY children.keywords.name == %@
The documentation on using predicates doesn't explicitly state that
this is even possible, and I fear it might not be.
If that is the case, then I had another thought about how to solve
this problem. Articles have ArticleGroups as their parent entity.
keywords is actually a relationship attribute for ArticleGroups, but
is always the empty set for ArticleGroups. Is there a nice way to
have each ArticleGroup return an amalgamation of their children's
keywords?
That is, suppose 'Solar' is an ArticleGroup with two Articles; 'ANU',
'UNSW'. ANU had keywords with name attributes 'photovoltaic' and
'university', and UNSW had keywords 'university' and 'thermal'. Then
Solar's returned keywords would be 'university', 'photovoltaic' and
'thermal'.
This would be easy if the keyword relationship were 1-to-many, as it
is easy to provide a custom accessor method for to-1 relationships.
The documentation implies that the only supported accessor method for
to-many relationships is mutableValueForKey: or valueForKey: neither
of which I particular want to override in ArticleGroup as I'd have to
undo the override for the child entity Article.
Any thoughts?
Cheers and thanks in advance,
Arved von Brasch
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