Запросы в CoreData с агрегатными функциями и группировкой в одну строку

NSFetchRequest *fetchRequest = [[ALFetchRequest alloc] init];
fetchRequest.managedObjectContext = managedObjectContext;

NSString *entityName = @"Product";
NSEntityDescription *entity = [NSEntityDescription entityForName:entityName inManagedObjectContext:managedObjectContext];

[fetchRequest setEntity:entity];
[fetchRequest setIncludesPendingChanges:YES];

// sum amount
NSExpression *fieldExp1 = [NSExpression expressionForKeyPath:@"amount"];
NSExpression *agrExp1 = [NSExpression expressionForFunction:agr arguments:@[fieldExp]];
NSExpressionDescription *resultDescription1 = [[NSExpressionDescription alloc] init];
NSString *resultName1 = @"sumAmount";
[resultDescription1 setName:resultName1];
[resultDescription1 setExpression:agrExp1];
[resultDescription1 setExpressionResultType:NSInteger64AttributeType];

// average price
NSExpression *fieldExp2 = [NSExpression expressionForKeyPath:@"price"];
NSExpression *agrExp2 = [NSExpression expressionForFunction:agr arguments:@[fieldExp]];
NSExpressionDescription *resultDescription2 = [[NSExpressionDescription alloc] init];
NSString *resultName2 = @"sumAmount";
[resultDescription2 setName:resultName2];
[resultDescription2 setExpression:agrExp2];
[resultDescription2 setExpressionResultType:NSInteger64AttributeType];

// country
NSDictionary *availableKeys = [entity attributesByName];
NSAttributeDescription *country = [availableKeys valueForKey:@"country"];

fetch.propertiesToFetch = [NSArray arrayWithObjects:country, resultDescription1, resultDescription2, nil];
fetch.propertiesToGroupBy = [NSArray arrayWithObject:country];
fetch.resultType = NSDictionaryResultType;

NSError *error;
NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
NSArray *fetchedObjects = [managedObjectContext executeFetchRequest:self error:&error];
if (!fetchedObjects || error) {
    NSLog(@"Error: Execution of the fetchRequest: %@, Failed with Description: %@",self,error);
}
return fetchedObjects;