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Re: Core Data: right way to gather all elements of a to-many relationship?
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Re: Core Data: right way to gather all elements of a to-many relationship?


  • Subject: Re: Core Data: right way to gather all elements of a to-many relationship?
  • From: Luke Evans <email@hidden>
  • Date: Wed, 11 Feb 2009 14:09:52 -0800

 The documentation (Core Data Programming Guide --> Managed Object
Accessor Methods --> Custom To-Many Relationship Accessor Methods)
spells out all the stipulations for custom to-many accessors and the
code example is:

@property NSSet *employees;

 ... without the readonly flag. I would not expect this to hand back
an array versus a set, but I would also not specify a to-many
relationship as a read-only property.


Yes, and it seems that it's OK to set an _entire_ set for a to-many relationship using the simple pattern:
parent.elements = <some NSSet>
according to p.62 of the Core Data Programming Guide.


However, if one wants to discourage this (and I do), then it seems like the right thing is to set the property as read-only (after all the docs say that the
property is only a wrapper "to suppress compiler warnings", around the dynamic KVC handling in NSManagedObject itself).


The "dynamically generated accessor methods" (things like - addElementsObject and -removeElementsObject) are described on p.44 of the Guide
(which in turn references documentation for mutableSetValueForKey:).


Anyway, like you, I can't see how having a read-only flag on the wrapping property in my NSManagedObject subclass is going to affect
how a to-many relationship is internally represented within NSManagedObject. Moreover, I reset the declaration of the property to the unquestionably
canonical "@property(retain) NSSet *elements" and the problem still manifests. The "retain" appears to be required for use with GC as the default is "assign"
which will cause warnings.


-- lwe

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  • Follow-Ups:
    • Re: Core Data: right way to gather all elements of a to-many relationship?
      • From: "I. Savant" <email@hidden>
References: 
 >Core Data: right way to gather all elements of a to-many relationship? (From: Luke Evans <email@hidden>)
 >Re: Core Data: right way to gather all elements of a to-many relationship? (From: "I. Savant" <email@hidden>)
 >Re: Core Data: right way to gather all elements of a to-many relationship? (From: Luke Evans <email@hidden>)
 >Re: Core Data: right way to gather all elements of a to-many relationship? (From: "I. Savant" <email@hidden>)

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