Question

Say I’m modeling a school, so I have 2 Entities: Student and Class. For whatever reason, I want each class roster to have a custom sort order. In a simple relationship, this would mean giving Student a sortOrder attribute and just sorting the list by this number. Issue is, a Student might be order 3 in one Class and order 6 in another. How would I store these orderings in Core Data in a way that I can easily access them and sort my lists properly?

 Student                  Class
 classes  <<--------->>  students
    ^                       ^
    |                       |
unordered                ordered

This diagram might help explain what I’m trying to do. The students “roster” I would want to be fetched in a specific order stored somewhere, which could be any ordering. Storing this ordering is what I’m not sure how to do in a way that’s the most efficient. Creating a bunch of Order objects and trying to manage the links sounds like a lot of overhead, and it feels like there must be a better way.

Answer 1

Student <<->> StudentClass <<->> Class

StudentClass
----
studentID
order
classID 

Then you can select as necessary.

For example, you have a student. Fetch all StudentClass where StudentID is student.studentID. You then have the order, as well as access to the Class.

You’ll likely want to add some business logic to make your life easier. Also, if you’re not already using it, take a peek at MOGenerator: https://github.com/rentzsch/mogenerator

EDIT: I’d really like to know why this is getting voted down. Comments would be much appreciated.