you can use -
//your code as it is till this line but with
//NSSortDescriptor *sort = [[NSSortDescriptor alloc]
initWithKey:@"messageId" ascending:NO];
NSArray* dataArray = [[managedObjectContext executeFetchRequest:fetchRequest error:&error] mutableCopy];
NSArray *sortedArray;
sortedArray = [dataArray sortedArrayUsingComparator:^NSComparisonResult(id a, id b) {
NSString *first = [(Messages*)a messageId];
NSString *second = [(Messages*)b messageId];
return [first compare:second];
}];
for (Messages* msg in sortedArray) {
//your code
}
Happy coding :P