-(NSArray*)entityName:(NSString*)entityName findManyByRelation:(NSDictionary*)dict
{
//  TODO handle dict nil and emptyness
    NSMutableArray *arr = [[NSMutableArray alloc] initWithCapacity:dict.count];
    for(NSString *key in dict)
    {
        NSExpression *left = [NSExpression expressionForKeyPath:key];
        NSExpression *right = [NSExpression expressionForConstantValue:[dict objectForKey:key]];
        NSComparisonPredicate *cp = [[NSComparisonPredicate alloc] initWithLeftExpression:left
            rightExpression:right modifier:NSDirectPredicateModifier type:NSEqualToPredicateOperatorType options:0];
        [arr addObject:cp];
        [cp release];
    }
    NSPredicate *pred = nil;
    if(arr.count == 1)
        pred = [[arr objectAtIndex:0] retain];    // why do I have to retain here?
    else
        pred = [[NSCompoundPredicate alloc] initWithType:NSAndPredicateType subpredicates:arr];
 
    NSFetchRequest *fr = [[NSFetchRequest alloc] init];
    fr.entity = [NSEntityDescription entityForName:entityName inManagedObjectContext:self];
    fr.predicate = pred;
    [arr release];
    [pred release];
//	NSLog(@"predicate effective: %@", fr.predicate);
 
    NSError *err = nil;
    NSArray *ps = [self executeFetchRequest:fr error:&err];
    if(err != nil)
        [NSException raise:@"DB Error" format:@"Fetch problem %@", fr.predicate.predicateFormat];
    [fr release];
    return ps;
}

-(NSManagedObject*)entityName:(NSString*)entityName findByPrimaryKey:(NSDictionary*)dict
{
    NSArray *ps = [self entityName:entityName findManyByRelation:dict];
    if(ps == nil || ps.count == 0)
        return nil;
    if (ps.count == 1)
        return [ps objectAtIndex:0];
    [NSException raise:@"DB Error" format:@"Multiple hits for %@", dict];
    return (NSManagedObject*)1/0;
}

-(NSManagedObject*)entityName:(NSString*)entityName selectOrInsertWithKey:(NSDictionary*)dict
{
    NSManagedObject *o = [self entityName:entityName findByPrimaryKey:dict];
    if(o == nil)
    {
        NSEntityDescription *ed = [NSEntityDescription entityForName:entityName inManagedObjectContext:self];
        o = [[NSManagedObject alloc] initWithEntity:ed insertIntoManagedObjectContext:self];
        for(NSString *key in dict)
            [o setValue:[dict objectForKey:key] forKey:key];
        [o autorelease];
    }
    return o;
}

+(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];
}

NSURL *storeUrl = [NSURL fileURLWithPath:
[[self applicationDocumentsDirectory]
stringByAppendingPathComponent: @"CoreDataDemo.sqlite"]];