Using NSPredicate to search NSArray attribute of core data entity

Question

I've searched far and wide to find a solution to this problem. All of my attempts result in 0 results. Here is the general data structures:

Core Data Entity A {
  stringAttribute string
  ....
  transformableAttribute(NSArray of NSString objects) keywords
}

where keywords = [NSArray arrayWithObjects:@"string 1",@"string 2",@"string 3",nil]

I'm trying to run a predicate to search the NSArray transformable attribute.

I've tried the following against entity A. The core data store is a sqlite store.

NSString *term = @"string 1";
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"ANY keywords like[cd] %@", term];

----> Results in 0 matches

NSArray *termArray = [NSArray arrayWithObject:@"string 1"];
NSPredicate *predicate = [NSPredicate predicateWithFormat@"ANY keywords in %@", termArray];

----> Results in 0 matches

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SUBQUERY(keywords, $x, $x like %@).@count > 0", term]

----> Results in an error that a non-relationship cannot be a subquery collection

I've tried some permutations of the above, but still no results. Any advice? Is this possible with Core data?

Thanks!

I think life would be easier if you made your array of strings a separate entity and use a relationship to connect them. What you are trying to do is easy if implemented like that. — agilityvision
– agilityvision, Commented Jan 13, 2012 at 4:10
Yeah, I think a separate entity is best, just like in SQL. I was hoping to avoid doing a migration, but I can't find a better way. I'm using fetchedresutlscontrollers, which require fetching by predicate, and I can't filter manually. — John Denver
– John Denver, Commented Jan 13, 2012 at 6:28

Vincent Bernier · Accepted Answer · 2012-01-13 04:08:12Z

0

I'm not use with transformableAttribute that is an element of Core Data that I haven't got into, but if I recall you can't predicate on them. (so If I'm wrong please some one call me on this)

But when I see that your transformableAttribute is an array of string I just want to say why do you want an array in a database?

Why not make a relationship? A one to many relationship if your array can have different number of string.

Core Data is an abstraction of a Data Base, in a DB you don't use array, you use tables. That would probably simplify your life and make the fetching possible.

answered Jan 13, 2012 at 4:08

Vincent Bernier

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1 Comment

John Denver Over a year ago

This seems to be true. When I do a direct search on NSPredicate with transformableAttribute, many folks have found that you can't do it. The transformable attribute is stored in the DB as binary data, so doing a SQL query on it won't work.

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