Hello All,
I'm trying to query a Core Data database which contains geoLocation information
for all of the objects of type "Photo" which are within a specified distance of
a target point, using the following code.
- (NSArray*) photosNearLatitude: (NSNumber*) inLatitude
longitude: (NSNumber*) inLongitude
{
NSExpression *theLHS = [NSExpression expressionForFunction: [NSExpression
expressionForEvaluatedObject]
selectorName:
@"distanceFromLatitude:longitude:"
arguments: [NSArray
arrayWithObjects:
[NSExpression
expressionForConstantValue: inLatitude],
[NSExpression
expressionForConstantValue: inLongitude],
nil]];
NSExpression* theRHS = [NSExpression expressionForConstantValue: [NSNumber
numberWithDouble: 0.1]];
NSPredicate* thePredicate = [NSComparisonPredicate
predicateWithLeftExpression: theLHS
rightExpression: theRHS
modifier: NSDirectPredicateModifier
type: NSLessThanOrEqualToPredicateOperatorType
options: 0];
NSManagedObjectContext* theManagedObjectContext = [self managedObjectContext];
NSFetchRequest* theFetch = [[[NSFetchRequest alloc] init] autorelease];
theFetch.entity = [NSEntityDescription entityForName: @"Photo"
inManagedObjectContext:
theManagedObjectContext];
theFetch.predicate = thePredicate;
NSError* theError = NULL;
NSArray* theResults = [theManagedObjectContext executeFetchRequest: theFetch
error:
&theError];
return theResults;
}
The "Photo" class has the following selector.
- (NSNumber*) distanceFromLatitude: (NSNumber*) inLatitude
longitude: (NSNumber*) inLongitude
My problem is that when I call "executeFetchRequest", an exception occurs:
2009-11-25 16:55:20.633 Serendipity[8498:a0f] Unsupported function expression
FUNCTION(SELF, "distanceFromLatitude:longitude:" , 47.71283333333334, -122.225)
-[Photo distanceFromLatitude:longitude:] is never called.
Can anyone suggest what might be going wrong?
- Ron Aldrich
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