Re: Unique items in Core Data models
Re: Unique items in Core Data models
- Subject: Re: Unique items in Core Data models
- From: mmalc crawford <email@hidden>
- Date: Mon, 14 May 2007 23:05:57 -0700
On May 14, 2007, at 6:50 PM, Sam Stigler wrote:
I just found the section on "Faulting and Uniquing" in Apple's Core
Data Programming Guide; that looks like it might have what you're
looking for.
No, that explains how Core Data ensures that, for any given managed
object context there is no more than one managed object corresponding
to any given record in the persistent store.
That's a good question.... you'd hope so, considering that it's
based on SQLite....
Core Data is *not* "based on SQLite". SQLite is one of the persistent
store formats supported by Core Data (see <http://developer.apple.com/documentation/Cocoa/Conceptual/CoreData/Articles/cdPersistentStores.html
> -- see also <http://developer.apple.com/documentation/Cocoa/Conceptual/CoreData/Articles/cdBasics.html
>).
You might have more luck in a search for this if you use the term
"key" instead of "unique item" -- in relational database terms, what
you want is for the title to be the key. (Seehttp://en.wikipedia.org/wiki/Relational_database#Keys.)
No! Absolutely not. Primary key and unique value are different
things. Something may not be a primary key and yet need to be
unique. Typically a primary key should be a simple integer value.
Core Data does not provide a mechanism to unique attribute values.
Uniquing attributes is typically an expensive and sometimes difficult
thing to do. The basic way is to execute a fetch prior to assigning a
value (the fetch predicate being <nameOfUniqueAttribute> == newValue;
you want the count of the returned array to be 0).
mmalc
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