Re: Need some help with fetch requests
Re: Need some help with fetch requests
- Subject: Re: Need some help with fetch requests
- From: Chris Hanson <email@hidden>
- Date: Fri, 1 Feb 2008 12:36:37 -0800
On Feb 1, 2008, at 12:03 PM, Carter R. Harrison wrote:
Today I'm working with NSFetchRequests for the first time and I need
some help learning how to filter down the initial set of managed
objects that I want to search against.
Entity: File
Relationship: Messages
I assume you actually mean "messages" given that properties of objects
in Objective-C start with lower-case letters. :)
My initial thought was to add more criteria to my predicate to help
narrow down the search base, but I'm not sure how the predicate's
criteria could traverse relationships.
Magic. :)
Do all of your relationships have appropriate inverses? If not, they
should. Then you could just use a predicate like this:
NSPredicate *fieldSearchPredicate = [NSPredicate predicateWithFormat:
@"(message.file IN %@) AND (value = %@)", files,
requestedFieldValue];
Use that in a fetch request on the Field entity and it should just
work. "files" should be an NSArray or NSSet of instances of your File
entity, or NSManagedObjectID instances representing instances of your
File entity.
-- Chris
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