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 following information:
name | rate | factor |
_______|______|________|
John | 3.2 | 4 |
Betty | 5.5 | 7 |
Betty | 2.1 | 2 |
Betty | 3.1 | 2 |
Edward | 4.5 | 5 |
John | 2.3 | 4 |
How would i set up the request to return an array with just: John, Betty, Edward?
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<NSFetchRequestResult>(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] }
}