The query optimiser for NSPredicate queries ontop CoreData/SQLite on the iPhone is a bit rudimentary (cough) and so I had to optimise myself to get binary-search enabled quick results:
+(NSPredicate*)findBySearchTerm:(NSString*)rawTerm within:(BOOL)within context:(NSManagedObjectContext*)context
{
NSSet *tokens = [MovieM indexTokens:rawTerm];
if(tokens == nil || tokens.count < = 0)
return [NSPredicate predicateWithFormat:@"FALSEPREDICATE"];
NSMutableArray *preds = [NSMutableArray arrayWithCapacity:tokens.count];
if(within == NO && context != nil)
{
// As queries aren't optimised by default we do it ourselves:
// 1st: find matching entries from the IndexKey table - leveraging it's index:
NSFetchRequest *fr = [[NSFetchRequest alloc] init];
fr.entity = [NSEntityDescription entityForName:@"IndexKey" inManagedObjectContext:context];
NSMutableSet *result = nil;
NSError *error = nil;
for(NSString *token in tokens)
{
// BETWEEN uses the table-index while BEGINSWITH does not:
fr.predicate = [NSPredicate predicateWithFormat:@"key BETWEEN {%@, %@}", token, [MovieM upperBoundSearchString:token]];
NSArray *keys = [context executeFetchRequest:fr error:&error];
if(error != nil)
NSLog(@"Oops: %@", error);
// turn IndexKey entries to movies (join up):
NSArray *movs = [keys valueForKey:@"movie"];
// aggregate the results for each token:
if(result == nil)
result = [NSMutableSet setWithArray:movs];
else
[result intersectSet:[NSSet setWithArray:movs]];
}
[fr release];
return [NSPredicate predicateWithFormat:@"SELF IN %@", result];
}
NSPredicate *template = nil;
if(within)
template = [NSPredicate predicateWithFormat:@"ANY index.key CONTAiNS $searchTerm"];
else
template = [NSPredicate predicateWithFormat:@"ANY index.key BEGINSWITH $searchTerm"];
for(NSString *token in tokens)
{
NSDictionary *params = [NSDictionary dictionaryWithObject:token forKey:@"searchTerm"];
[preds addObject:[template predicateWithSubstitutionVariables:params]];
}
return [NSCompoundPredicate andPredicateWithSubpredicates:preds];
}
Helpers herein are
[MovieM indexTokens:rawTerm]folds diacritics and uppercase and cuts at whitespace or interpunction,[MovieM upperBoundSearchString:token]which was inspired by Apple Sample Code „DerivedProperty“NormalizedStringTransformer::upperBoundSearchString:.