On Apr 22, 2009, at 02:12, Mike Abdullah wrote:
On 22 Apr 2009, at 08:48, Ben Trumbull wrote:
Of course, why Apple couldn't have then added automatic support
for in-memory matching as the second step I don't know
Probably because nobody ever cared enough to file an enhancement
request, and it didn't occur to us that writing 1 line of code to
call filteredArrayWithPredicate was so troublesome.
Calling -filteredArrayWithPredicate is no hassle, but for a large
predicate, it has the bad performance of comparing a bunch of the
persistent properties all over again, despite already knowing
they'll match the predicate. Since I assume Core Data must do some
kind of internal splitting up of the predicate in order to perform
its fetch, I'd have thought it is in a good position to know what
the remaining transient portion of the predicate is.
You assume incorrectly.
CoreData simply translates the predicate to SQL and passes it down to
SQLite as a WHERE clause. Hence the lack of support for transient
properties: SQLite has no idea what to do when you ask it to qualify
by a column that doesn't exist in its schema.
+Melissa
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