Hello! I’m develping a school gradebook app, and I’m having trouble getting CoreData to work. I have two entities, Student and Activity, and array controllers in IB. Both entities have attributes and relationships to each other. In IB I have a table with two columns: student and grade. The table’s connected to the student array controller. Another table holds a list of activities, connected to the activities array controller. What I want to do is have the grade column show the respective students’ grade for the selected activity, and change when selection of activity changes. I’ve tried everything I can think of. Is there an easy way to do this? Thanks, –LoganCollins

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This seems like a popular homebrew application. I am writing one for my father’s use at the moment (4 June 2006). From my experience it is an excellent way to get a thorough understanding of CoreData, InterfaceBuilder, and CocoaBindings.

Here are the aspects of the development that I will cover:

*Maintaining common Activities with separate grading per Student *Populating tables using InterfaceBuilder (IB) and CocoaBindings

Maintaining common Activities with separate grading per Student

First, the Data Model needs to be changed. I suggest adding a bridging object, Report, between Students and Activities to your Data Model. Here are the Data Model changes I suggest to achieve that:

(Entity)Student:

[…whatever attributes and relationships you need otherwise] *relationship(Report 0..)reports(inverse student)

(Entity)Activity:

[…whatever attributes and relationships you need otherwise] *attribute(String)name** attribute(Decimal)weight *relationship(Report 0..)reports(inverse activity)

(Entity)Report:

*[…whatever attributes and relationships you need otherwise] *attribute(Decimal)mark *relationship(Student)student(inverse reports) *relationship(Activity)activityactivity(inverse **reports)

I use the following algorithm to programmatically generate Reports for Students across a set of common Activities (I am using your terminology rather than mine for clarity):

Activity custom NSManagedObject subclass:

function awakeOnInsert for each student in fetch of all Students create new Report relate the new Report’s activity to this Actity relate the new Report’s student to the student of this iteration add the new Report to student of this iteration’s list of reports

Student custom NSManagedObject subclass:

function awakeOnInsert for each activity in fetch of all Activities create new Report relate the new Report’s student to this Student relate the new Report’s activity to the activity of this iteration add the new Report to this Student’s list of reports

Populating tables using InterfaceBuilder (IB) and CocoaBindings

To get the Reports to show up in InterfaceBuilder you will need a new ArrayController for Report entities (that has managedObjectContext bound to File’s Owner’s managedObjectContext key) and whose contentSet is bound to the Student ArrayController’s controller key selection and model key reports.

(NSArrayController)Students:

*Entity: (Student) *managedObjectContext: File’s Owner model key managedObjectContext

(NSArrayController)ReportsForSelectedStudent:

*managedObjectContext: File’s Owner model key managedObjectContext *contentSet: Students controller key selection model key reports

With these NSArrayController’s you can now bind a table called Reports in your Student record view with columns Activity, Mark, and Weight as follows:

Reports table in Student view:

*Activity column value binding: ReportsForSelectedStudent controller key arrangedObjects model key reports.name *Mark column value binding: ReportsForSelectedStudent controller key arrangedObjects model key mark *Weight column value binding: ReportsForSelectedStudent controller key arrangedObjects model key weight

I hope this helps. Please contact me if you are having trouble. My contact info is on my profile page linked below.

–AlainODea (4 June 2006) *