Swift CoreData using predicates with Array

Question

I need to keep array of Strings in CoreData and later on use predicates for filtering data for that array.

According to this post field type Transformable (with custom class [String]) does the trick and I can properly save array of Strings: How to save Array to CoreData?

However, I can't use predicates for this fields. Specifically, my goal is to find all items where at least one item in saved array matches pattern.

So, back to question: is there a good way of storing array in CoreData so that I can apply predicates for it later on?

Possible duplicate of https://stackoverflow.com/questions/6104566/core-data-transformable-attributes-not-working-with-nspredicate. — Martin R, Oct 06 '18 at 10:47
Yes, that post somehow answers. I can't use it however since not familiar with Objective-C — Олександр Бабіч, Oct 06 '18 at 11:05
Another possible solution - to create another Entity with possible array values and create relations between my object and new entities. — Олександр Бабіч, Oct 06 '18 at 11:07

score 2 · Accepted Answer · edited Jul 27 '21 at 17:20

Found an appropriate solution for CoreData

Don't put array as Transformable field in Entity

Create separate Entity with a single field, use that entities instead of array.
Create relation between main Entity and Array replacement Entity.
During runtime: find CoreObject of array Entity using predicate:

NSPredicate(
    format: "%K = %@", #keyPath(YourArrayEntity.onlyField),
    matchingString
)

Use predicates for searching your main entities

NSPredicate(
    format: "ANY %K == %@",
    #keyPath(YourMainEntity.relationToArrayEntity), 
    arrayEntityFoundInPreviousStep
)

Swift CoreData using predicates with Array

1 Answers1