Convert NSPredicate into NSDictionary for use as a query string in an AFNetworking HTTP request

foo.m

- (NSURLRequest *)requestForFetchRequest:(NSFetchRequest *)fetchRequest
                             withContext:(NSManagedObjectContext *)context {
    
    // init the query string dictionary
    NSMutableDictionary *queryString = nil;
    
    // if we're given a predicate, convert it to a dictionary
    if (fetchRequest.predicate) {
        
        if ([fetchRequest.predicate isKindOfClass:[NSCompoundPredicate class]]) {
            
            // init the query string
            queryString = [[NSMutableDictionary alloc] init];
            
            // get the predicate
            NSCompoundPredicate *predicate = (NSCompoundPredicate *)fetchRequest.predicate;
            
            // set the query string values
            for (NSComparisonPredicate *comparison in predicate.subpredicates) {
                
                [queryString setValue:comparison.rightExpression.constantValue forKey:comparison.leftExpression.keyPath];
                
            }
            
        } else if ([fetchRequest.predicate isKindOfClass:[NSComparisonPredicate class]]) {
            
            // init the query string
            queryString = [[NSMutableDictionary alloc] init];
            
            // get the predicate
            NSComparisonPredicate *predicate = (NSComparisonPredicate *)fetchRequest.predicate;
            
            // set the query string values
            [queryString setValue:predicate.rightExpression.constantValue forKey:predicate.leftExpression.keyPath];
            
        }
        
    }
    
    return [self requestWithMethod:@"GET" path:[self pathForEntity:fetchRequest.entity] parameters:queryString];
    
}