Firebase function in firebase function - swift

Question

The following function has to return all of my users's friends list. However it only does it for one of the friends. I know this is because the 2 firebase functions are running async, however I am not sure what I have to change the function so that it runs the way is should. That is retrieve all friends.
///retrieves all of user's friends
func fetchFriends(completion: #escaping ([FriendModel])->()){
FRIEND_REQ_REF.child(CURRENT_USER_ID).observe(.childAdded, with: {(snapshot) in
var friends = [FriendModel]()
if snapshot.value as? Int == 0 {
self.USERS_REF.child(snapshot.key).observeSingleEvent(of: .value, with: {(snap) in
if let dictionary = snap.value as? [String : AnyObject]{
let friend = FriendModel()
friend.setValue(dictionary["userName"], forKey: "userName")
friend.setValue(dictionary["name"], forKey: "name")
friends.append(friend)
completion(friends)
}
})
}
})
}
this is my data structure:
FRIEND_REQ_REF
firebaseUserID
friendFirebasegivenID : 0
anotherFriendFirebasegivenID : 0
USERS_REF
friendFirebasegivenID
userName : String
name : String
anotherFriendFirebasegivenID : 0
userName : String
name : String

Answer 1

///retrieves all of user's friends
func fetchFriends(completion: #escaping ([FriendModel])->()){
FRIEND_REQ_REF.child(CURRENT_USER_ID).observe(.value, with: {(snapshot) in
var friends = [FriendModel]()
if let dict = snapshot.value as? [String : AnyObject] {
for (_,k) in dict.enumerated() {
if k.value == 0 {
self.USERS_REF.child(k.key).observeSingleEvent(of: .value, with: {(snap) in
if let dictionary = snap.value as? [String : AnyObject]{
let friend = FriendModel()
friend.setValue(dictionary["userName"], forKey: "userName")
friend.setValue(dictionary["name"], forKey: "name")
friends.append(friend)
completion(friends)
}
})
}
}
}
})
}