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 <c...@me.com>: > On Mar 19, 2009, at 1:26 AM, tmow...@talktalk.net 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 > > _______________________________________________ > > Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) > > Please do not post admin requests or moderator comments to the list. > Contact the moderators at cocoa-dev-admins(at)lists.apple.com > > Help/Unsubscribe/Update your Subscription: > http://lists.apple.com/mailman/options/cocoa-dev/micpringle%40gmail.com > > This email sent to micprin...@gmail.com > _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
