Getting only first object from Firebase Snapshot Swift - swift

Question

So this is my Firebase Structure:
I'm trying to get all books pictures (bookImage), add them to list and then use this list to fill a table or anythings else. (I'm using swift 3)
struct item {
let picture: String!}
var items = [item]()
func getLatestAddedItems(){
let databaseRef = FIRDatabase.database().reference()
databaseRef.child("Items").observe(.childAdded, with: {
FIRDataSnapshot in
let picture = (FIRDataSnapshot.value as? NSDictionary)?["bookImage"] as? String ?? ""
//self.items.insert(item(picture: picture), at: 0)
self.items.append(item(picture: picture))
print(self.items[0].picture)
print(self.items[1].picture) // error here
})}
I'm able to see the first print output but on the second one I'm getting fatal error: Index out of range even I have 3 books on my database.

Answer 1

Since your using .childAdded, it iterates through that closure for each object in the data tree, in this case, each book. When you try to print the second picture, its still in its first iteration. Meaning you only have retrieved the first book so far. That's why you can print the first book item but not the second one. If you moved the print statements outside of the closure, and then did the print statements after the closure iterated over all three books, you wouldn't get the error.
Don't change it to .value unless if every time a new one is subsequently added you want to get the entire list of books all over again. If its a large amount of books, it will be a lot of data to go through each time.
Summary: .childAdded gives you one book at a time, with a new snapshot for each one. .value gives you all the books in one snapshot, then you must iterate over them yourself in the closure. ex.
for snap in snapshot.children {
// now you can do something with each individual item
}
also I just noticed your using the FIRDataSnapshot type in your closure, that should be a variable which represents the snapshot you received, not the type itself. Change "FIRDataSnapshot in" to something like "snapshot in" snapshot is a representation of what information was given to you by the observe closure, in this case, an object with a type of FIRDataSnapshot.
Edit:
Your solution you mentioned below works fine, but I'll add an alternative that is cleaner and easier to use.
add an init method to your Book class that takes a FIRDataSnapshot as the init parameter, then init the object when you query Firebase:
struct Book {
let bookImageString: String
init?(snapshot: FIRDataSnapshot) {
guard let snap = snapshot.value as? [String : AnyObject], let urlString = snap["bookImage"] else { return nil }
bookImageString = imageString
{
{
then when you query firebase you can do this:
for snap in snapshot.children {
if let snap = snap as? FIRDataSnapshot, let book = Book(snapshot: snap) {
self.items.append(book)
{
}
doing it this way cleans up the code a little bit and leaves less chance of error in the code.
Also, since your using .value, make sure to empty the data source array at the beginning of the closer, or else you will get duplicates when new books are added.
items.removeAll()

Answer 2

Finally I'm posting the solution:
func getLatestAddedItems(){
let databaseRef = FIRDatabase.database().reference()
databaseRef.child("Items").observe(.value, with: {
snapshot in
//self.items.insert(item(picture: picture), at: 0)
for childSnap in snapshot.children.allObjects {
let snap = childSnap as! FIRDataSnapshot
print(snap.key)
let picture = (snap.value as? NSDictionary)?["bookImage"] as? String ?? ""
print(picture)
}
})
}