Re: Relationships during awakeFromInsert

FROM : Mike Rossetti
DATE : Sat Feb 02 23:59:59 2008

Thanks to Ben for helping me figure 'it' out.

On Feb 2, 2008, at 1:11 AM, Ben Trumbull wrote:
>> [snip]
>> What I'm seeing is that self.myMOA is 'nil' in this 
>> awakeFromInsert, so apparently the relationship has not yet been 
>> established.

>
> MOB just got allocated.  The -initWithEntity... method is usually 
> still on the stack frame.  It doesn't have a .myMOA yet.  It's not 
> clear from your description why one would expect otherwise.


This gets to the crux of the matter: None of the NSManagedObject 
describe at what point in the life-cycle of such an object the 
relationships are established.  It's as surprising that there are no 
accommodations for intercepting the object at a point where it has 
been completely assembled along with its relationships--even a 
notification would help and perhaps 
NSManagedObjectContextObjectsDidChangeNotification would do the trick.

Making the job even more difficult is that the example implementation 
in the "NSPersistentDocument Core Data Tutorial" leads to some 
assumptions because it is just such a stripped-down, simplified example.

The problem is that the relationships have not yet been established 
when awakeFromInsert is called.  My attempts to use delayed 
notifications or intercept setValue... also failed.

Here is the solution, taking the example in the tutorial as a base and 
using 'employee' in place of my MOB:

1. In the nib file for the editor window, bind the department 
NSObjectController's 'Content Object' to the File's Owner (MyDocument) 
'department' instance.
2. Still in the nib, bind the employees' NSArrayController's 'Content 
Set' to the department's NSObjectController's selection/employees.
3. Back in the model (xdatamodel) select the 'department' relationship 
of the 'employee' box, pop up the contextual menu, and select the Copy 
Method Implementations to Clipboard option.
4. Go the Employee.m and paste to the bottom of the file.
5. Move the CoreDataGeneratedPrimitiveAccessors interface portion to 
the top of the file.
6. Add an #import "Department.h".
7. Move the setDepartment function up into the implementation section 
and add any code to it for initialization of the employee based on the 
department.
8. Rip out the department function and the validateDepartment function.


>> Where can I set MOB's 'seeded' using MOA's 'seed'?

>
> Presumably you have some code somewhere that does something like:
> NSManagedObject* MOB = [NSEntityDescription 
> insertNewObjectForEntityForName:@"MOB" inManagedObjectContext:moc];


This simple application (which is a stripped down version of the one 
used in the Core Data Tutorial) simply connects the 'Add MOB' button 
to the NSArrayController in the nib and uses the default 'Add' 
selector of the array controller.  So, no, there is no code like that.

> Right after that would work.
>
> If you have a reference to MOA during -awakeFromInsert (like in a 
> global, or through the appDelegate),


In this case, since I'm following the pattern shown in the 
"NSPersistentDocument Core Data Tutorial" and have a document a global 
wouldn't be appropriate.

where the document has a single instance of an MOA,

> and doing things the easy way doesn't work, you could do something 
> like -performSelector:... afterDelay:0 or in response to the MOC's 
> NSManagedObjectContextObjectsDidChangeNotification.


That would have been my next step if I hadn't stumbled upon the (now 
obvious) customization of relationship management possibilities.

Thanks again,
Mike