Core data, how to get NSManagedObject's ObjectId when NSFetchRequest returns NSDictionaryResultType?
Yes you can, using the very nifty but badly-documented NSExpressionDescription
class. You need to add a properly-configured NSExpressionDescription
object to the array of NSPropertyDescription
objects you set via setPropertiesToFetch:
for your NSFetchRequest
.
For example:
NSExpressionDescription* objectIdDesc = [[NSExpressionDescription new] autorelease];
objectIdDesc.name = @"objectID";
objectIdDesc.expression = [NSExpression expressionForEvaluatedObject];
objectIdDesc.expressionResultType = NSObjectIDAttributeType;
myFetchRequest.propertiesToFetch = [NSArray arrayWithObjects:objectIdDesc, anotherPropertyDesc, yetAnotherPropertyDesc, nil];
NSArray* fetchResults = [myContext executeFetchRequest:myFetchRequest error:&fetchError];
You should then have a @"objectID"
key in the the dictionaries you get back from your fetch request.
NSFetchRequest *request = [[NSFetchRequest alloc] init];
request.entity = [NSEntityDescription entityForName:@"yourEntity" inManagedObjectContext:context];
request.sortDescriptors = [NSArray arrayWithObjects:[NSSortDescriptor sortDescriptorWithKey:@"title" ascending:YES], nil];
request.predicate = nil;
request.fetchLimit = 20;
NSError *error = nil;
NSArray fetchedResults = [context executeFetchRequest:request error:&error];
NSLog(@"%@", [fetchedResults valueForKey:@"objectID"]);
Since your fetched results are already in an array why not pull them out with the valueForKey:@"objectID" ? Clean, simple only need one fetch request so you can pull all other data you need as well.