Getting values from Firebase snapshot in Swift - swift

Question

Im successfully getting data from Firebase but I can't manage to push it into array to use. My database is as follows:
users
-Wc1EtcYzZSMPCtWZ8wRb8RzNXqg2
-email : "mike#gmail.com"
-lists
-LJiezOzfDrqmd-hnoH-
-owner: Wc1EtcYzZSMPCtWZ8wRb8RzNXqg2
-LJif-UgPgbdGSHYgjY6
-owner: Wc1EtcYzZSMPCtWZ8wRb8RzNXqg2
shopping-lists
-LJh6sdBJtBCM7DwxPRy
-name: "weekly shopping"
-owner: "mike#gmail.com"
I have a home page after login that shows existing shopping lists on table if they exist. On viewDidLoad() I get shopping list IDs from the user and use those IDs as a reference to get details from shopping-lists.
However, I cant manage to save these data into an array as it gets deleted after closure. How can I do that in a clean way?
override func viewDidLoad() {
super.viewDidLoad()
SVProgressHUD.show()
tableView.allowsMultipleSelectionDuringEditing = false
// Sets user variable - must have
Auth.auth().addStateDidChangeListener { auth, user in
guard let user = user else { return }
self.user = User(authData: user)
// If new user, write into Firebase
self.usersRef.observeSingleEvent(of: .value, with: { snapshot in
if !snapshot.hasChild(self.user.uid) {
self.usersRef.child(user.uid).setValue(["email": user.email!])
}
})
// Get shopping lists data from "users/lists"
self.usersRef.child(user.uid).child("lists").observe(.value, with: { snapshot in
// Get list IDs
if snapshot.exists() {
if let result = snapshot.children.allObjects as? [DataSnapshot] {
for child in result {
self.listNames.append(child.key)
}
}
}
// Use list IDs - to get details
for item in self.listNames {
let itemRef = self.shoppingListsRef.child(item)
itemRef.observeSingleEvent(of: .childAdded, with: { (snapshot) in
if let value = snapshot.value as? [String: Any] {
let name = value["name"] as? String ?? ""
let owner = value["owner"] as? String ?? ""
let shoppingList = ShoppingList(name: name, owner: owner)
self.items.append(shoppingList)
}
})
}
})
self.tableView.reloadData()
SVProgressHUD.dismiss()
}
}

Answer 1

(the question is a bit unclear so several parts to this answer to cover all possibilities. This is Swift 4, Firebase 4/5)
You don't really need to query here since you know which nodes you want by their key and they will always be read in the in order of your listNames array. This assumes self.listNames are the keys you want to read in.
for item in listNames {
let itemRef = shoppingListsRef.child(item)
itemRef.observe(.value, with: { (snapshot) in
if let value = snapshot.value as? [String: Any] {
let name = value["name"] as? String ?? ""
let owner = value["owner"] as? String ?? ""
print(name, owner)
}
})
}
Generally, queries are used when you are searching for something within a node - for example if you were looking for the node that contained a child name of 'weekly shopping'. Other than that, stick with just reading the nodes directly as it's faster and has less overhead. Keep reading...
I also removed the older NSDictionary and went with the Swift [String: Any] and modified your error checking
However, the real issue is reading that node with an .observe by .value. Remember that .value reads in all children of the node and then the children need to be iterated over to get each separate DataSnapshot. Also, .observe leaves an observer on the node notifying the app of changes, which I don't think you want. So this will answer the question as posted, (and needs better error checking)
for item in listNames {
let queryRef = shoppingListsRef
.queryOrdered(byChild: "name")
.queryEqual(toValue: item)
queryRef.observe(.value, with: { (snapshot) in
for child in snapshot.children { //even though there is only 1 child
let snap = child as! DataSnapshot
let dict = snap.value as! [String: Any]
let name = dict["name"] as? String ?? ""
let owner = dict["owner"] as? String ?? ""
print(name, owner)
}
})
}
And the answer...
This is probably more what you want...
for item in listNames {
let queryRef = shoppingListsRef
.queryOrdered(byChild: "name")
.queryEqual(toValue: item)
queryRef.observeSingleEvent(of: .childAdded, with: { snapshot in
let dict = snapshot.value as! [String: Any]
let name = dict["name"] as? String ?? ""
let owner = dict["owner"] as? String ?? ""
print(name, owner)
})
}
note the .childAdded instead of .value which presents the snapshot as a single DataSnapshot and doesn't need to be iterated over and the .observeSingleEvent which does not leave an observer attached to each node.
Edit
Based on additonal information, it would be best too change the structure to this
shopping-lists
-LJh6sdBJtBCM7DwxPRy
-name: "weekly shopping"
-uid: "Wc1EtcYzZSMPCtWZ8wRb8RzNXqg2"
and then when the user logs in just query the shopping lists node for any uid that's theirs.