[Leopard] SUBQUERY predicate with CoreData
-
I have an example CoreData managed object model that contains an
entity Foo{fooProp:string; keyValues:{to- m,eany relationship to
KeyValue}) and an entity KeyValue(key:string,value:float; foo:{to-one
relationship to Foo}). I'm having trouble executing a fetch request
with a predicate that contains a SUBQUERY expression on a managed
object context using this model. I've included the .xcdatamodel (zip'd
with an added extension -- hopefully it will make it pass the list
filter). In the Xcode "CoreData application", using the included
.xcdatamodel and adding this method to the app delegate:
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
// add some examples to the XML store
id foo = [NSEntityDescription insertNewObjectForEntityForName:@"Foo"
inManagedObjectContext:[self managedObjectContext]];
[foo setFooProp:@"fooProp1"];
id kv = [NSEntityDescription insertNewObjectForEntityForName:@"KeyValue"
inManagedObjectContext:[self
managedObjectContext]];
[kv setKey:@"key1"];
[kv setValue:[NSNumber numberWithFloat:1.0] forKey:@"floatValue"];
[foo addKeyValuesObject:kv];
foo = [NSEntityDescription insertNewObjectForEntityForName:@"Foo"
inManagedObjectContext:[self managedObjectContext]];
[foo setFooProp:@"fooProp2"];
kv = [NSEntityDescription insertNewObjectForEntityForName:@"KeyValue"
inManagedObjectContext:[self
managedObjectContext]];
[kv setKey:@"key2"];
[kv setValue:[NSNumber numberWithFloat:2.0] forKey:@"floatValue"];
[foo addKeyValuesObject:kv];
NSFetchRequest *fetch = [[[NSFetchRequest alloc] init] autorelease];
[fetch setEntity:[NSEntityDescription entityForName:@"Foo"
inManagedObjectContext:[self
managedObjectContext]]];
[fetch setPredicate:[NSPredicate
predicateWithFormat:@"(SUBQUERY(self.keyValues, $kv, $kv.key like
'key1' && $kv.floatValue==1.0).count > 0) && fooProp like
'fooProp1'"]];
id result = [[self managedObjectContext] executeFetchRequest:fetch
error:nil]; //app crashes here
NSLog(@"%@", result);
}
produces the following (relevant) output at the console
*** -[NSCFArray compare:]: unrecognized selector sent to instance 0x195220
and the application crashes during the [[self managedObjectContext]
executeFetchRequest:fetch error:nil] method.
I know the documentation on using SUBQUERY is still on the way, but I
was hoping that one of the CoreData gurus could suggest what I'm doing
wrong.
Thanks!
Barry -
On Feb 4, 2008, at 14:02, Barry Wark wrote:> "(SUBQUERY(self.keyValues, $kv, $kv.key like 'key1' &&
> $kv.floatValue==1.0).count > 0) && fooProp like 'fooProp1'"]];
>
should be:
"(SUBQUERY(self.keyValues, $kv, $kv.key like 'key1' &&
$kv.floatValue==1.0)<....> > 0) && fooProp like 'fooProp1'"]]; -
> [fetch setPredicate:[NSPredicate
> predicateWithFormat:@"(SUBQUERY(self.keyValues, $kv, $kv.key like
> 'key1' && $kv.floatValue==1.0).count > 0) && fooProp like
> 'fooProp1'"]];
A SUBQUERY expression produces an array of results, a lot like
NSArray's -filteredArrayWithPredicate:
Tacking on .count at the end is adding a keypath. Basically it's like
[subqueryResults valueForKeyPath:@"count"]
NSArray responds to the keypath .count by invoking -count on each
element and giving you back an array of all the counts. This array
is not happy being compared to a scalar 0.
NSArray responds to the keypath "@count" in the manner you want. You
can use either
"(SUBQUERY(self.keyValues, $kv, $kv.key like 'key1' &&
$kv.floatValue==1.0)<....> > 0)"
or
"(SUBQUERY(self.keyValues, $kv, $kv.key like 'key1' &&
$kv.floatValue==1.0)[size] > 0)"
where the second form is using some of the built-in predicate
operators for aggregates.
--
-Ben -
Thank you to Ben and Melissa for setting me straight. I notice that
the NSExpression documentation gives
"SUBQUERY(residents, $x, $x.firstname == "Jane" && $x.lastname ==
"Doe").count != 0)"
as an example subquery for a similar use case. Besides the missing
opening '(', this example has the, as I know now, incorrect use of
.count != 0 pattern. Is this well known, or worth filing a bug for the
documentation?
Thanks,
Barry
On Feb 4, 2008 3:29 PM, Ben Trumbull <trumbull...> wrote:>> [fetch setPredicate:[NSPredicate
>> predicateWithFormat:@"(SUBQUERY(self.keyValues, $kv, $kv.key like
>> 'key1' && $kv.floatValue==1.0).count > 0) && fooProp like
>> 'fooProp1'"]];
>
> A SUBQUERY expression produces an array of results, a lot like
> NSArray's -filteredArrayWithPredicate:
>
> Tacking on .count at the end is adding a keypath. Basically it's like
> [subqueryResults valueForKeyPath:@"count"]
>
> NSArray responds to the keypath .count by invoking -count on each
> element and giving you back an array of all the counts. This array
> is not happy being compared to a scalar 0.
>
> NSArray responds to the keypath "@count" in the manner you want. You
> can use either
>
> "(SUBQUERY(self.keyValues, $kv, $kv.key like 'key1' &&
> $kv.floatValue==1.0)<....> > 0)"
>
> or
>
> "(SUBQUERY(self.keyValues, $kv, $kv.key like 'key1' &&
> $kv.floatValue==1.0)[size] > 0)"
>
> where the second form is using some of the built-in predicate
> operators for aggregates.
> --
>
> -Ben
> -
On Feb 4, 2008, at 8:00 PM, Barry Wark wrote:> Is this well known, or worth filing a bug for the
> documentation?
There's no problem with always filing a bug if you notice it. That
way there's no question as to whether the doc team knows about it.
--
I.S.
