The relationship between Homework and Subject is currently a one-to-one relationship (as seen that you have 1 arrow pointing to the word homework and 1 arrow pointing to newRelationship). To add multiple homework objects to a subject, change the relationship to a one-to-many relationship.
Schedule *schedule;
Homework *homework;
for (Homework *homework in schedule.homework) {
NSLog(@"homework = %@", homework);
}
[schedule addHomeworkObject:homework];