Re: Need some help with fetch requests

FROM : Carter R. Harrison
DATE : Fri Feb 01 21:41:05 2008

On Feb 1, 2008, at 3:36 PM, Chris Hanson wrote:

> 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. :)


You assumed correctly.  Thanks for making a note of this though.

>
>

>> 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.
>


Excellent!  I had already made inverse relationship so your answer 
should work.  I'm not sure why I couldn't figure that out, but I do 
appreciate it!

>  -- Chris
>