Re: Core Data, questions about two models in an application
Re: Core Data, questions about two models in an application
- Subject: Re: Core Data, questions about two models in an application
- From: Dan Treiman <email@hidden>
- Date: Mon, 17 Jul 2006 10:22:46 -0500
If you have managed objects that are not saved in documents, you'll
need another persistent store to save them in. This is basically a
combination of the "Core Data Application", and the "Core Data
Document Based Application".
For information about how to manage relationships across persistent
stores, check out:
http://developer.apple.com/documentation/Cocoa/Conceptual/CoreData/
Articles/cdUsingMOs.html
particularly in the section on Managed Object IDs and URIs:
"You can use object IDs to define “weak” relationships across
persistent stores (where no hard join is possible)."
To do this you'll have to write accessors, and methods for managing
deletion - core data has no built-in way to define relationships
across persistent stores.
-Dan
On Jul 17, 2006, at 7:43 AM, rakel wrote:
E.g. let there be a Variable called with title "Operating System".
Then the person with name "Piglet" can have a Value for this
Variable with the "valueData" attribute set to "Windows" and the
person "Winnie the Pooh" can have a Value for the same Variable
with "valueData" attribute set to "Mac OS X".
One way is to start with a "Core Data Application" in XCode and
have one data model with the entities Person, Value and Variable
(this is how I currently do it).
Now to my question:
Another way could be to use a "Core Data Document Based
Application" where each person is represented by one document. But
since the Variables doesn't belong to any specific person, the
Variable data cannot be part of the documents. Hence I would need
two models, one model for the meta data and one model for the
person data. Data for the "person data model" would be saved with
each document. Data for the "meta data model" would be saved
"somewhere else". Also, there must be a connection between the
Value entity in the "person model" and the Variable entity in the
"meta data model".
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