Array Controller sort descriptors vs. SQLite data store (was Re: localized compare and SQLite persistent store)
Array Controller sort descriptors vs. SQLite data store (was Re: localized compare and SQLite persistent store)
- Subject: Array Controller sort descriptors vs. SQLite data store (was Re: localized compare and SQLite persistent store)
- From: Jim Correia <email@hidden>
- Date: Wed, 7 Sep 2005 11:35:25 -0400
On Aug 11, 2005, at 4:20 PM, Melissa Turner wrote:
Short answer:
Because the SQL store doesn't know anything about
localizedCaseInsensitiveCompare:
Longer explanation:
When your array controller pulls its contents from the database, it
does so using an NSFetchRequest with the entity you are requesting,
any predicate you have set to specify which instances of that
entity you want, and any sort descriptors you have set to describe
how the data should be brought back.
In the XML, binary and in memory stores, the evaluation of the
predicate and sort descriptors happens in memory, where we have
full access to the obj-C runtime, Cocoa, and all the goodness
therein, including the comparison methods on NSString.
The SQL store on the other hand, compiles the predicate and sort
descriptors to SQL, and evaluates the result in the database
itself. This is done primarily for speed; databases are much faster
at this, it's what they're designed for. But it means that
evaluation is happening in a non-Cocoa world, and so sort
descriptors (or predicates) which rely on Cocoa simply can't work,
and result in exceptions like the one you're seeing.
You may need to subclass NSArrayController so you can have it not
pass the sort descriptors to the database and do the sorting after
your data has been fetched instead.
Do you have an example?
Or recommendations for a more general solution?
Is it a simple matter of overriding - (BOOL)fetchWithRequest:
(NSFetchRequest *)fetchRequest merge:(BOOL)merge error:(NSError **)
error; ?
I've been using the XML store since the documentation recommends it
for debugging, but just switched over to the SQLite store (which I
intend to ship with) to see what the fallout was. That the sort
descriptors are applied in the database and not afterwards generates
problems for me in a few places right off the bat:
1) an NSTableView which was using localizedCaseInsensitiveCompare:
for the columns
2) derived attributes
I have a "source list" for which I've manually set the sort
descriptors based on name and priority. Priority isn't a model
attribute, but a constant returned from a KVC compliant method based
on the object type.
Upon loading the UI, the controller fetches and logs
2005-09-07 11:28:08.782 Organizer[1820] *** NSRunLoop ignoring
exception 'unresolved keypath: priority' that raised during posting
of delayed perform with target 4c2b20 and selector 'invokeWithTarget:'
Was this problem previously considered? Proposed solution?
Thanks,
Jim
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