Re: How do you store an NSArray as an attribute in a Core Data entity
Re: How do you store an NSArray as an attribute in a Core Data entity
- Subject: Re: How do you store an NSArray as an attribute in a Core Data entity
- From: Mic Pringle <email@hidden>
- Date: Thu, 19 Mar 2009 12:10:47 +0000
Have a look at the following ...
http://developer.apple.com/documentation/Cocoa/Conceptual/CoreData/Articles/cdNSAttributes.html#//apple_ref/doc/uid/TP40001919
-Mic
2009/3/19 Chris Hanson <email@hidden>:
> On Mar 19, 2009, at 1:26 AM, email@hidden wrote:
>
>> I want to store a list of Strings as an attribute of an entity in Core
>> Data but there doesn't appear to be a way to use NSArray (or NSSet or
>> NSDictionary either) as an attribute.?Please can someone explain how you use
>> an NSArray or NSDictionary as an attribute of a Core Data entity?
>
> In general, if you want to have multiple things as an attribute of a Core
> Data entity, what you really want is a to-many relationship with another
> entity.
>
> Let's take tags as an example. Say I'm creating a weblog editor and I want
> the ability to tag my posts. I could model this as a string attribute with
> some specific format (space- or comma-separated), or as a transformed
> attribute. However, that doesn't get me the ability to do things like say
> "show all the posts with this tag" or even "auto-complete known tags." It
> also leads to persistent store bloat because I'm breaking a cardinal rule of
> relational data, "store each piece of data once," because each tagged post
> winds up with a copy of the tag's text.
>
> Instead of having an attribute, I would model a to-many relationship from my
> Post entity to my new Tag entity, with a to-many inverse relationship from
> my Tag entity to my BlogPost entity. This way:
>
> Each Tag instance only exists once in the persistent store.
> I can traverse the object graph between Posts and Tags, and between Tags and
> Posts, with ease.
> I can perform interesting queries across both Posts and Tags to improve my
> user experience (e.g. support auto-completion or generate tag clouds).
> Not having Tags stored directly on Posts means if I'm just dealing with a
> Post, Core Data won't bother fetching the Tags too.
>
> Entities and relationships are good, hope this helps you leverage them!
>
> -- Chris
>
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