Question

Suppose a Manager has a to-many relationship with Employee objects. Given a reference to a Manager object (i.e. NSManagedObject *manager), how do I get a reference to “the Employee with the lowest salary among all of those whose salaries exceed 10000″?

I can think of two possible approaches:

Approach 1: constructing an NSFetchRequest and specifying the Manager wanted with the object ID of the Manager in question.

Approach 2: some kind of key-value coding expression on Manager, e.g. [manager valueForKeyPath:@"..."] (with some use of NSPredicate?)

I’m inclined towards Approach 2 if there’s a plausible solution. Please enlighten me.

Answer 1

You can filter your array of Employee relationship to get the one you want.
1) First, get all the Employee with salaries over 10000:

NSArray *filtered = [manager.employees filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"(salary > 10000)"]];

2)Then sort it in descending order

NSSortDescriptor* sortOrder = [NSSortDescriptor sortDescriptorWithKey: @"salary" ascending: NO];
NSArray *sortedAndFiltered =  [filtered sortedArrayUsingDescriptors: [NSArray arrayWithObject: sortOrder]];

3)Then just get your employee

[sortedAndFiltered lastObject];