On 2009 Apr 20, at 04:50, Jerry Krinock wrote:
Problem solved
But there's an even better way. Upon further study of the Predicate Programming Guide, I find that there are even more limitations to Core Data fetches with predicates. The most troubling is that:
"The Core Data SQL store supports only one to-many operation per query; therefore in any predicate sent to the SQL store, there may be only one operator (and one instance of that operator) from ALL, ANY, and IN."
A much better way appears to be to fetch all objects from the store with no predicate and then use -[NSArray filteredArrayWithPredicate:]. This takes only one more line of code, solves all problems, and is supposedly cheaper too:
"If you use the Core Data framework, the array methods provide an efficient means of filtering an existing array of objects without —- as a fetch does —- requiring a round trip to a persistent data store."
Furthermore, now since my left-side expressions don't need to be managed properties I don't need the categories -- I can just add simple derived-attribute getters to my target object class and predicate upon the derived attribute directly.
So, I guess the reason why Apple has never noticed that "Core Data Fetches + Transient Properties + NSPredicateEditor = Sadness" is because there's a better way to do it.
Makes me wonder why NSFetchRequest even supports a predicate, since its predicate has all these limitations and is supposedly more expensive when compared to fetching all objects and then using - [NSArray filteredArrayWithPredicate:] ? It would have saved me a day on the learning curve had it not been there for me to hang myself with.
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