Swift - Get one-to-many relationship - ios

Question

let's imagine that we have 2 entities:
-People (name, age, ..)
-House (color)
we recorded the data several times with house.addToPeople (newPeople) for each house
we want to get all the people of the house colored blue
how do we fetch this?
I tried this code but it gets all the people
let appD = UIApplication.shared.delegate as! AppDelegate
let context = appD.persistentContainer.viewContext
let peopleFetch = NSFetchRequest<NSFetchRequestResult>(entityName: "People")
let houseFetch = NSFetchRequest<NSFetchRequestResult>(entityName: "House")
houseFetch.fetchLimit = 1
houseFetch.predicate = NSPredicate(format: "color = %#", "blue")
...
let res = try? context.fetch(peopleFetch)
let resultData = res as! [People]
how to do this ?

Answer 1

Try this function. What it does is fetching all of the People and creating an array with all of the results.
func getAllItems() -> [People]? {
let request = NSFetchRequest<NSFetchRequestResult>(entityName: "People")
request.returnsObjectsAsFaults = false
do {
let result: NSArray = try context.fetch(request) as NSArray
return (result as? [People])!
} catch let error {
print("Errore recupero informazioni dal context \n \(error)")
}
return nil
}
If you want to perform your search following certain criteria such as a color, use the following code after request:
//Here i'm searching by index, if you need guidance for your case don't hesitate asking
request.predicate = NSPredicate(format: "index = %d", currentItem.index)
Edit: actually the code above is just to get all of the people, if you want to base your search on the houses do the following:
func retrieve()-> [People]{
//Fetch all of the houses with a certain name
let houseRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "House")
houseRequest.predicate = NSPredicate(format: "name = %#", "newName") //This seearch is by name
houseRequest.returnsObjectsAsFaults = false
do {
//put the fetched items in an array
let result: NSArray = try context.fetch(houseRequest) as NSArray
let houses = result as? [Houses]
//Get the people from the previous array
let people: [People]? = (houses.people!.allObjects as! [People])
return people
} catch let error {
print("Errore recupero informazioni dal context \n \((error))")
}
return nil
}

Answer 2

Thank you for your answer !
In this example "houses" is an array, so we have to add an index ➔ houses[0].people!.AllObjects
And thank you very much for your explanation.