HI Sean,
One example would be if you have a method that calculates a value.
That value would not be in the DB so the compiled predicate (if it
would even compile) would not work because there is not column
corresponding to your calc'd value.
I think this is worth filing a bug against the docs to clear that up.
HTH,
-bd-
http://bill.dudney.net/roller/objc
On May 16, 2008, at 3:50 PM, Sean McBride wrote:
Hi all,
After reading the docs and archives, it is clear to me now that with
Core Data's SQL store one is more limited in the types of predicates
one
can use with fetches.
What I can't find is a list of what I can and can't do. The best I
found was "[the] SQL store, on the other hand, compiles the predicate
[...] to SQL and evaluates the result in the database itself. [...] it
means that evaluation happens in a non-Cocoa environment, and so sort
descriptors (or predicates) that rely on Cocoa cannot work". How do I
know if my predicate "relies on Cocoa"?
For example, given the Employees/Departments scenario: if I try to
fetch
all employees that are in exactly 2 departments I use a fetch
predicate
of "departments[SIZE] == 2" which works great everywhere except with
the
SQL store. I learnt this the hard way.
Thanks,
--
____________________________________________________________
Sean McBride, B. Eng [EMAIL PROTECTED]
Rogue Research www.rogue-research.com
Mac Software Developer Montréal, Québec, Canada
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