Re: Core data transformer direction
Re: Core data transformer direction
- Subject: Re: Core data transformer direction
- From: mmalc crawford <email@hidden>
- Date: Wed, 02 Jul 2008 23:37:39 -0700
On Jul 2, 2008, at 10:15 PM, Quincey Morris wrote:
... Core Data uses an instance of NSValueTransformer to convert the
attribute to and from an instance of NSData. Core Data then stores
the data instance to the persistent store. By default, Core Data
uses the NSKeyedUnarchiveFromDataTransformerName transformer,
however you can specify your own transformer if you want.
... If you specify a custom transformer, it must transform an
instance of the non-standard data type into an instance of NSData
and support reverse transformation.
The first paragraph (and the description of
NSKeyedUnarchiveFromDataTransformerName) says that the forward
transformation is NSData->SomeClass.
The second paragraph says that the forward transformation is
SomeClass->NSData.
It's not clear in what way the first paragraph "says that the forward
transformation is NSData->SomeClass" -- it states that the transformer
is used "to convert the attribute to and from an instance of NSData"
-- at worst it's ambiguous. The second paragraph makes a definite
statement that is unambiguous.
See also:
<http://developer.apple.com/documentation/Cocoa/Reference/CoreDataFramework/Classes/NSAttributeDescription_Class/Reference/Reference.html#//apple_ref/doc/uid/TP30001175-SW3
>
mmalc
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