Relationships loop with Core Data

Question

I had a conceptual problem with Core Data.

I have an entity called OBJ which has an OBJ entity in a relationship. I get very eloquent messages like "An error occured." when I test my model.

For each OBJ entity, I wish to define one or more ACTIONs associated with another OBJ entity. So I guess my mistake comes from a loop, but not sure.

At first, I defined an inverse relationship (as advised by the doc, a relationship should always have its inverse):

ENTITY OBJ
Attributes:
name    
status
Relationships:
actions
<-------- >>

ENTITY ACTION    
Attributes:
name   
Relationships:
obj

Well, it does not work, because the OBJ always refers to itself. I have therefore decoupled relationships. The ACTION points to an OBJ and the OBJ points to several ACTIONs, without reciprocity. Error message.

My basic idea is that each of the ACTIONs associated with a particular OBJ can run if the status of another OBJ allows it.

How to build this to be MVC consistent? The basic idea seems simple, it is his achievement that is less so. Is it a wrong Core Data modeling? Do I make a mistake at the controller level? Interface? Note that at this level I have not written a single line of code.

Thank you!

What is relation between the objects? Is it parent/child? – Eimantas Sep 20 '12 at 13:08 — Eimantas, Sep 20 '12 at 13:08

score 1 · Accepted Answer · answered Sep 20 '12 at 13:00

1

If you want to

define one or more ACTIONS associated with another OBJ

it means that one OBJ can have many ACTIONS and one ACTION can have many OBJs.

Therefore you should define a relationship between ACTION and OBJ that is to-many in both directions.

OBJ.actions <<-------->> ACTION.obj

Unless you intend to have "sub-objects" (such as CATEGORY and subCATEGORY) you should not have a relationship between OBJ and OBJ.

answered Sep 20 '12 at 13:00

Mundi

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Ok for this, Mundi, thanks for pointing out my first conception error. I wanted to avoid a OBJ<-->OBJ relation so I created the ACTION entity. But it's clear for me now that I was confusing ACTION as entity (to-many relationship) with an action instance (to-one relationship). Now for the bindings… I get this:[<_NSFaultingMutableSet 0x101d48970> addObserver:forKeyPath:options:context:] is not supported. Key path: alias when I try to set the Selected Value of the controller to the object of the action. – berfis Sep 20 '12 at 15:29
Don't quite understand your second problem. Maybe open another question? – Mundi Sep 20 '12 at 21:02
Ok, follow me on "Core Data to-many relationship Controller". – berfis Sep 20 '12 at 21:18

score 0 · Answer 2 · answered Sep 22 '12 at 10:58

I found a solution by adding a new relationship between "OBJ" and "ACTION".

OBJ                           ACTION
…                             …
Relationships                 Relationships
targetObject     <------->>   actions
conditionObject  <------->>   condition

If I don't, the inverse relationship always refers to the same (self) object. So, by changing a relationship, I was changing the object itself!

By adding a new one-to-many relationship, I can indirectly make a OBJ to OBJ relation (the targetObject and conditionObject may be the same one) AND keep the graph consistent.

Each day, I understand better what "Core Data is not for beginners" means…

Relationships loop with Core Data

2 Answers2