create a Compound Predicate in coreData xcode iphone
You can use a compound predicate:
NSPredicate *p1 = [NSPredicate predicateWithFormat:@"studentsToClass.className = %@", @"5th"];
NSPredicate *p2 = [NSPredicate predicateWithFormat:@"studentsToExamRecord.result = %@", @"Pass"];
NSPredicate *p = [NSCompoundPredicate andPredicateWithSubpredicates: @[p1, p2]];
Or you simply combine the tests with "AND":
NSPredicate *p = [NSPredicate predicateWithFormat:@"studentsToClass.className = %@ AND studentsToExamRecord.result = %@",
@"5th", @"Pass"];
Note that the argument list of predicateWithFormat
is not nil
-terminated.
The number of arguments is determined by the number of format specifiers in the format
string.
First, you shouldn't really call the student - class
relation studentsToClass
. The name of the relation should reflect what type of object is at the other end.
E.g.
In this case the Student
relation to Class
should be called class
because the object there is a single Class
entity.
The inverse relation should not be called classToStudent
it should be called students
because the object there is a NSSet
of multiple Students
.
EDIT
Just to add to this. The name of the relation should explain WHY it is there. We can see that the relation is from class to student but if you call it "classToStudent" it doesn't explain anything. Also, what if you have a second relation from class to student? What do you call that. If you call it attendees
or pupils
or attendingStudents
etc.. it gives the relation meaning.
SOLUTION
In this example I'm going to call them how I would call them and you will see it makes it a bit easier to understand...
Anyway...
NSPredicate *classPredicate = [NSPredicate predicateWithFormat:@"class.className = %@", @"5th"];
NSPredicate *passPredicate = [NSPredicate predicateWithFormat:@"result.name = %@", @"Pass"];
NSCompoundPredicate *compoundPredicate = [NSCompoundPredicate andPredicateWithSubpredicates:@[classPredicate, passPredicate]];