Array in object from data model comes nil - ios

Question

I have a model class called Coupon and it has an array of objects called Array!
When I create an object from from Coupon class the array inside of this object comes nil and it gets an error. What am I doing wrong?
class Coupon {
private var _date: String!
private var _editor: String!
private var _predictions: Array<Prediction>?
var date: String {
get {
return _date
}
}
var editor: String {
get {
return _editor
}
}
var predictions: Array<Prediction>? {
get {
return _predictions
}
set {
self._predictions = predictions
}
}
}
And the controller is as follows: c.predictions![0] gives nil error
let ref = DataService.ds.REF_COUPONS.queryOrdered(byChild: "date")
ref.observe(.childAdded, with: { (snapshot) in
if let couponDict = snapshot.value as? Dictionary<String, AnyObject> {
let c_key = snapshot.key
let c = Coupon(couponKey: c_key, couponData: couponDict)
let childSnapShot = snapshot.childSnapshot(forPath: "predictions")
if let snapshots = childSnapShot.children.allObjects as? [FIRDataSnapshot] {
for snap in snapshots{
let p_key = snap.key
let p = Prediction(predictionKey: p_key, predictionData: snap.value as! Dictionary<String, AnyObject>)
self.predictions.append(p)
c.predictions![0] = self.predictions[0] <--- ERROR LINE
}
}
self.coupons.append(c)
}
self.couponsTableView.reloadData()
})

Answer 1

Because it's value is nil by default. So predictions! will result in trying to unwrap an optional whose value is nil kind of error.
You should create new array there:
c.predictions = [self.predictions[0]]
Also there is no need for backing fields in swift. Your Coupon class can be reduced to:
class Coupon {
private(set) var date: String!
private(set) var editor: String!
var predictions: Array<Prediction>?
}
private(set) means that the value can only be set within this class.
The definition line of predictions var predictions: Array<Prediction>? can be replaced to have default value of empty array:
class Coupon {
private(set) var date: String!
private(set) var editor: String!
var predictions: [Prediction] = []
}
[Prediction] is same as Array<Prediction>
Once it has default value of empty array instead of creating new array you can safely append to it:
c.predictions.append(self.predictions[0])
Also note that your code c.predictions[0] = self.predictions[0] would work never even in this case because the array is defaulted to empty has not 0th element.

Answer 2

When you create the class Coupon with let c = Coupon(couponKey: c_key, couponData: couponDict) your array is not initialize, so that's normal to have an error when you are trying to use it in the line c.predictions![0] = self.predictions[0] <--- ERROR LINE, your object Coupon you could initialize the array predictions as an empty array like this
class Coupon {
private var _date: String!
private var _editor: String!
private var _predictions = [Prediction]()

Answer 3

Element in predictions array at index 0 doesn't exist, so you can't replace it with new element. I suggest you to replace _predictions array with empty predictions array
var predictions = [Prediction]()
then you can append new element to this array like this:
c.predictions.append(self.predictions[0])
Also in your case there is no need to use property with getter and setter and you can also use struct instead of class
struct Coupon {
var date: String
var editor: String
var predictions = [Prediction]()
// your convenience init
}