CoreData get distinct values of Attribute

Question

I\'m trying to setup my NSFetchRequest to core data to retrieve the unique values for a specific attribute in an entity. i.e.

an entity with the follow

Answer 1

This is a simple approach in Swift 5.x:

// 1. Set the column name you want distinct values for
let column = "name"

// 2. Get the NSManagedObjectContext, for example:
let moc = persistentContainer.viewContext

// 3. Create the request for your entity
let request = NSFetchRequest(entityName: "User")

// 4. Use the only result type allowed for getting distinct values
request.resultType = .dictionaryResultType

// 5. Set that you want distinct results
request.returnsDistinctResults = true

// 6. Set the column you want to fetch
request.propertiesToFetch = [column]

// 7. Execute the request. You'll get an array of dictionaries with the column
// as the name and the distinct value as the value
if let res = try? moc.fetch(request) as? [[String: String]] {
    print("res: \(res)")

    // 8. Extract the distinct values
    let distinctValues = res.compactMap { $0[column] }
}