NSPredicate, get results with a subset of one-to-many relationship - ios

Question

I'mm working around with Core Data and NSFetchedResultsController.
My Data Model looks like this:
Product with one-to-many relationship called dataLines.
The dataLine entity has a property name theWeek.
I want to fetch all Product where dataLines.theWeek == someValue. This is easily done with a subquery. But this returns all dataLines. Is it possible to create a NSPredicate that returns the Product and a subset if dataLines only with the dataLines == someValue?

Answer 1

What you want to achieve could be reached in two ways:
using a SUBQUERY
[NSPredicate predicateWithFormat:#"SUBQUERY(dataLines, $x, $x.theWeek == %#).#count > 0)", [NSNumber numberWithInt:18]];
or the ANY modifier
[NSPredicate predicateWithFormat:#"ANY dataLines.theWeek == %#", [NSNumber numberWithInt:18]];
You can do also the following if you need to check against multiple values:
[NSPredicate predicateWithFormat:#"SUBQUERY(dataLines, $x, $x.theWeek == %# or $x.theWeek == %#).#count > 0)", [NSNumber numberWithInt:18], [NSNumber numberWithInt:19]];
The same can be applied to ANY modifier. ANY ... OR ANY ....
Maybe if you share some code we could help you.
P.S. I suppose you don't use scalar values and theWeek is a number.
Hope it helps.

Answer 2

You should fetch the dataLine property instead.
Assuming your Product and dataLine entity connected by relationship someRelation then you can try this code;
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setEntity:[NSEntityDescription entityWithName:#"dataLine" inManagedObjectContext:self.managedObjectContext]];
[fetchRequest setPredicate:[NSPredicate predicateWithFormat:#"dataLines.week == %#",theWeek]];
NSMutableArray *tmpProduct [[NSMutableArray init] alloc];
NSMutableArray *tmpArray = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
for (dataLine *theDataLine in tmpArray);
NSLog(#"%#",theDataLine.someRelation.name);
tmpProduct = theDataLine.someRelation.name;
then you can just call tmpProduct to call or display your product in table view

Answer 3

Create a fetch request for the 'Product' entity:
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setEntity: [NSEntityDescription entityForName:#"Product" ...]]
then create a predicate using the properties/attributes of Product with 'ANY':
[fetchRequest setPredicate:
[NSPredicate predicateWithFormat:#"ANY dataLines.theWeek == %#", <whatever week>]];
then execute the fetch to get an array of Product with at least one <whatever week>.
Generally see 'Fetching Managed Objects', NSPredicate and related documentation.