Fetching a one to many relationship using Core Data

Question

iam a swift beginner, i wanna code a little app for me and i have a problem with it. My app has three entities (Templates, Records and Positions), here you can see:

Datamodel

At one part of the app i can add new Records and for that Record i add some Positions (xpos and ypos).

At a part I have a tableview were i list my Records. Now i wanna click one Record in the table and i want to get all Position-Attributes linked with the particular selected Record.

With that code i can get all xpos-Positions but how can i get a single xpos? :)

guard let moc = self.managedContext else {
   return
}

let fetchRequest: NSFetchRequest<Records> = Records.fetchRequest()

do {
   let searchResults = try moc.fetch(fetchRequest)
   let xpos = searchResults[0].positions?.mutableArrayValue(forKey: "xpos")
   print(xpos)
} catch {
   print("Error with request: \(error)")
}

skim skim · Accepted Answer · 2016-11-23T05:11:04

You want to look into using NSPredicate. NSPredicate basically lets you define the conditions which the record needs to meet to be included in the results. Think of it as a filter if you will.

fetchRequest.predicate = NSPredicate(format: "uniqueID = %@", arugments:...)

Fetching a one to many relationship using Core Data

1 Answers