On Mar 17, 2011, at 8:15 PM, Sandro Noël wrote: > Greetings! > > I am facing a problem with a complicated predicate I'm building. > ...
> then this predicate is fed to a fetch Request which in turn is fed to a > fetched Result Controller. > the fetch is configured to [fetchRequest setReturnsDistinctResults:YES]; > > The problem as stated in the introduction this complete predicate returns > multiple instances of the same record and it should not. About setReturnsDistinctResults: "If YES, the request returns only distinct values for the *fields specified by propertiesToFetch*." That is, setReturnDistinctResults: makes only sense IFF you also specified the set of properties you want to fetch (via -setPropertiesToFetch). And this requires that you specify NSDictionaryResultType for the resultType property of the fetch request. As a result, with setReturnDistinctResults:YES you get a set of dictionaries whose values are distinct. In other words, you cannot use -setReturnsDistinctResults:YES to make your result set distinct if this array contains *managed objects*. You might use a NSSet which you initialize from your original array of managed objects in order to get a unique set. Alternatively, you might fetch just objectID properties using a NSDictionaryResultType. This, however, is a bit elaborated: When you return (unique) dictionaries as objects in your result array, and if you want these dictionaries having a key "objectID" which value corresponds the actual managed object of this dictionary instance, you need to create an appropriate NSExpressionDescription: and include this property description in the array which you pass to -setPropertiesToFetch: NSExpressionDescription* objectIdDescription = [[NSExpressionDescription alloc] init]; [objectIdDescription setExpression:[NSExpression expressionForEvaluatedObject]]; [objectIdDescription setExpressionResultType:NSObjectIDAttributeType]; Note: NSExpressionDescription is subclassed from NSPropertyDescription. Then you use objectIdDescription as one of the properties (NSPropertyDescription) you want to fetch: [myFetchRequest setPropertiesToFetch:[NSArray arrayWithObject: objectIdDescription]]; Don't forget to set the result type (after you set the entity): [myFetchRequest setResultType: NSDictionaryResultType]; [myFetchRequest setReturnsDistinctResults:YES]; ... The next step would be to extract the objectIDs from the array of dictionaries and store them in an array for convenience. Regards Andreas > if any of you see a flaw in the logic or anything, please comment, I'm > currently so deep into it, I cant see it anymore. :) > > I hope I have not missed nay details. > Thank you!!! > Sandro. _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
