CoreData: Avoiding unresolved key path exception with SQLite store?
CoreData: Avoiding unresolved key path exception with SQLite store?
- Subject: CoreData: Avoiding unresolved key path exception with SQLite store?
- From: Jim Correia <email@hidden>
- Date: Wed, 5 Oct 2005 14:59:59 -0400
Previously Melissa Turner wrote:
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.
[...]
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.
What is the best way to avoid this problem?
Is there any hint I can give an NSFetchRequest that says if the fast
path through the SQL store doesn't work, please just do it the slower
way and don't bother me?
Is there a framework way to pick apart the sort descriptors or
predicate to see if all of the keyPaths are persistent attributes
(since plain old KV compliant keys, or transient attributes will
cause this error)?
Is there a way to catch the failure at runtime and fallback to the
old path in a custom subclass? The exception that is raised is an
NSInternalConsistencyException, so it doesn't appear very distinct
from other possible errors.
Or should I just give up and always do it the "slow" way (execute the
fetch request, then post process with the predicate and sort
descriptors) for any situation that could possibly cause this to arise?
Thanks,
Jim
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