CODEWITHSUNDEEP
swiftcore-data
mallowman
mallowman

Reputation: 211

Fetch attributes from to many relationship in Swift Core Data

I cannot for the life of me get this to work. I have a 'Match' entity and a 'Players' entity joined by a many-to-many relationship. For each match I am trying to create a string of names that are pulled from the Players entity in Core Data. Here is the latest incarnation of what I have been trying to achieve this with:

let players = matchData[indexPath.row].value(forKeyPath: "players") as? NSManagedObject
    let playerNames = players?.value(forKey: "firstName") as? NSMutableArray

    let playersString = playerNames?.componentsJoined(by: ",")

matchData is the NSManagedObject where my fetched data is held. "players" is the name of the relationship to the "Players" entity. And "firstName" is the attribute that I am trying to string together.

This however returns 'nil' for each match even though I know for sure that there are player records saved for each match. I can display other matchData items fine but am having trouble with this to-many relationship.

Upvotes: 1

Views: 579

Answers (1)

jrturton
jrturton

Reputation: 119242

value(forKeyPath: "players") as? NSManagedObject

If players is really a to-many relationship then this code will always return nil, because it will try to cast to an NSManagedObject but the actual type is a Set of NSManagedObjects.

value(forKeyPath: "players") as? Set<NSManagedObject> will get you past the first hurdle.

You'd be doing yourself a favour to specify managed object subclasses as well, then you'll have properties generated for all of these things which will make your code much cleaner and easier to understand.

Upvotes: 1

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