Core data relationship fault : null key

Question

I have an entity named Person that may have one home, and an entity named Home that may have one to N homes:

enter image description here

Then I have two array controllers:

Homes Controller, bound with managed object context, in entity mode: Home;
People Controller, bound with managed object context, in entity mode: person.

I have a cell based table view, bound with the People Controller.I am able to display successfully the first three columns (name, surname and age), but the problem is with the 4th column: the home's name.Inside the column there is a popup button cell, these are the bindings:

Content: Homes Controller.arrangedObjects ;
Content values: Homes Controller.arrangedObjects.name;
Selected object: People Controller.home.

The problem comes at runtime, when I try to click to the popup button to choose the home:

enter image description here

Like you see instead of the choice I see "Core data relationship fault", and if I try to change the home by clicking on the menu items, I see a lot of code printed to the console, I post only the most significant line:

2012-11-04 01:47:45.181 Test[4390:303] [<NSManagedObject 0x100156e60> valueForUndefinedKey:]: the entity Home is not key value coding-compliant for the key "(null)".

And after this the application freezes.

Edit: With some debug I am now able to know the state of the object when the exception occurs:

2012-11-09 02:42:02.495 Test[4650:303] <NSManagedObject: 0x100157460> (entity: Person; id: 0x10013d9d0 <x-coredata:///Person/t0182F6F4-9CCC-4F51-A82F-D00CE026DB752> ; data: {
    age = 20;
    home = "0x101953480 <x-coredata:///Home/t0182F6F4-9CCC-4F51-A82F-D00CE026DB753>";
    name = "New Name";
    surname = "New Surname";
})
2012-11-09 02:42:02.497 Test[4650:303] <NSManagedObject: 0x101953420> (entity: Home; id: 0x101953480 <x-coredata:///Home/t0182F6F4-9CCC-4F51-A82F-D00CE026DB753> ; data: {
    name = "New Home";
    people =     (
        "0x10013d9d0 <x-coredata:///Person/t0182F6F4-9CCC-4F51-A82F-D00CE026DB752>"
    );

It seems that the values are regular, there are not nil keys.I suspect the problem is with the bindings.

well what's the default value for a home's name. maybe that's not set and it is null? — Daij-Djan, Nov 08 '12 at 19:57
The default value is "New Home", indeed in the table view all the homes have already a name.But it says that Home does not respond for the key null.So probably in the bindings I am providing a key path which is nuull, but I don't understand what's wrong, name is not nil.So I bet that there's something wrong in the bindings. In the popup button the selected object is People Controller.home.Is that right? — Ramy Al Zuhouri, Nov 09 '12 at 00:10

score 5 · Accepted Answer · edited May 23 '17 at 12:00

It's hard to tell what is actually going on without seeing how you are fetching objects and their relationships from Core Data.

But, just because you see the word "fault" doesn't actually mean that there is a problem. A Core Data Fault just means that the data hasn't been retrieved from the store into the Managed Object Context yet.

Faults are very handy. They are like little stubs that stand in for objects in a relationship so that you don't pull too much into memory. It's only when you try to access the objects that they are swapped out for the actual objects.

See Core Data Relationship Fault for a bit more explanation.

I am doing all using cocoa binding, I thought it was all automatic, do I have to manually synchronize the database? — Ramy Al Zuhouri, Nov 12 '12 at 00:00

score 1 · Answer 2 · answered Nov 04 '12 at 03:09

1

Home-people and Person-home need to be declared as inverse relationships of one another using the model builder in order to function properly. The relationship will then appear as a single line.

answered Nov 04 '12 at 03:09

carmin

421
3
5

I forgot to say that: they're already the inverse of each other. – Ramy Al Zuhouri Nov 04 '12 at 11:39

Core data relationship fault : null key

2 Answers2