Re: Saving Images with Core Data (i.e., JPEG, TIFF, etc.)

FROM : mmalcolm crawford
DATE : Sat Apr 30 01:25:13 2005

On Apr 29, 2005, at 2:32 PM, Scott Ellsworth wrote:

>> Faulting only applies to relationships (so in your example 
>> comments will be loaded along with the other attributes on fetch), 
>> and is only really relevant if you use a SQLite store since it can 
>> fetch data on an as-needed basis.  The other stores -- XML and 
>> binary -- both load the whole persistent store into memory when 
>> they're accessed.

>
> What about fetched properties?  The docs imply a lazy fetch, but I 
> have not had a chance to test.
>

Fetched properties are fetched lazily, then cached.  If you want to 
update the cache, then (as with other updates) you refault the object.

> On the other hand, I am not sure I grok when I would use a fetched 
> property, as opposed to a stored fetch request.  Is there an 
> implicit "must be in a relatioship with the entity that the fetched 
> property is a part of" condition on a fetched property, or some such?
>

Think of how you might represent a smart playlists in iTunes.  You 
could use a fetch request in place of a fetched property, but this 
requires a different (and "explicit") code structure -- that is, 
you'll have to retrieve the fetch request from the model then execute 
it.  The fetched property specifies a relationship (albeit a weak 
one).  It's more natural to ask a (smart) Playlist for its Tracks 
than to create and execute a fetch request for Track to match a 
predicate.  Moreover, you then have to maintain the set of results 
yourself rather than it being associated with a particular Playlist...

mmalc