Ryan Ryan - 1 month ago 22
Swift Question

Firebase getting data in order

I am using Firebase and I have had no problems getting data in alphabetical order until recently. I never used queries, I always just used snapshots of data and sorted through them one-by-one. Recently, the data has not been always coming in alphabetical order in the snapVal. How do I make it so I get a snapVal of data sorted alphabetically, like it is in the snapshot from the database?

Real Example: there are 4 messages, id1-id4 (in that order). They contiain the message "1"-"4". The snapshot comes looking correct. But the snapVal (snapshot.value) looks like this:

["id2": {
DATE = "10/20/16";
"FIRST_NAME" = first;
ID = userID;
"LAST_NAME" = last;
MESSAGE = 2;
TIME = "8:12 PM";
}, "id4": {
DATE = "10/20/16";
"FIRST_NAME" = first;
ID = userID;
"LAST_NAME" = last;
MESSAGE = 4;
TIME = "8:12 PM";
}, "id1": {
DATE = "10/20/16";
"FIRST_NAME" = first;
ID = userID;
"LAST_NAME" = last;
MESSAGE = 1;
TIME = "8:12 PM";
}, "id3": {
DATE = "10/20/16";
"FIRST_NAME" = first;
ID = userID;
"LAST_NAME" = last;
MESSAGE = 3;
TIME = "8:12 PM";
}]


What the snapshot looks like:

["id1": {
DATE = "10/20/16";
"FIRST_NAME" = first;
ID = userID;
"LAST_NAME" = last;
MESSAGE = 1;
TIME = "8:12 PM";
}, "id2": {
DATE = "10/20/16";
"FIRST_NAME" = first;
ID = userID;
"LAST_NAME" = last;
MESSAGE = 2;
TIME = "8:12 PM";
}, "id3": {
DATE = "10/20/16";
"FIRST_NAME" = first;
ID = userID;
"LAST_NAME" = last;
MESSAGE = 3;
TIME = "8:12 PM";
}, "id4": {
DATE = "10/20/16";
"FIRST_NAME" = first;
ID = userID;
"LAST_NAME" = last;
MESSAGE = 4;
TIME = "8:12 PM";
}]


To get the snapVal, I use this:

if let snapVal = snapshot.value as? [String: AnyObject] {
// Comes out of order..
}


To clarify:

Snapshot (this ends up coming out correct):

Snap (CHAT) {
id1 = {
DATE = "10/20/16";
"FIRST_NAME" = first;
ID = userID;
"LAST_NAME" = last;
MESSAGE = 1;
TIME = "8:12 PM";
};
id2 = {
DATE = "10/20/16";
"FIRST_NAME" = first;
ID = userID;
"LAST_NAME" = last;
MESSAGE = 2;
TIME = "8:12 PM";
};
id3 = {
DATE = "10/20/16";
"FIRST_NAME" = first;
ID = userID;
"LAST_NAME" = last;
MESSAGE = 3;
TIME = "8:12 PM";
};
id4 = {
DATE = "10/20/16";
"FIRST_NAME" = first;
ID = userID;
"LAST_NAME" = last;
MESSAGE = 4;
TIME = "8:12 PM";
};
}


This is the output for
print(snapVal.keys)
inside
if let snapVal = snapshot.value as? [String: AnyObject]
:

LazyMapCollection<Dictionary<String, AnyObject>, String>(_base: ["id2": {
DATE = "10/20/16";
"FIRST_NAME" = first;
ID = userID;
"LAST_NAME" = last;
MESSAGE = 2;
TIME = "8:12 PM";
}, "id4": {
DATE = "10/20/16";
"FIRST_NAME" = first;
ID = userID;
"LAST_NAME" = last;
MESSAGE = 4;
TIME = "8:12 PM";
}, "id1": {
DATE = "10/20/16";
"FIRST_NAME" = first;
ID = userID;
"LAST_NAME" = last;
MESSAGE = 1;
TIME = "8:12 PM";
}, "id3": {
DATE = "10/20/16";
"FIRST_NAME" = first;
ID = userID;
"LAST_NAME" = last;
MESSAGE = 3;
TIME = "8:12 PM";
}], _transform: (Function))


My Code:

self.firebase.child("Chats").child(chatID).queryOrderedByKey().observeSingleEvent(of: .value, with: { (snapshot) in
print(snapshot)
if let snapVal = snapshot.value as? [String: AnyObject] {

print(snapVal)

for c in snapVal {
print("checking Message as child")
let message = c.value["MESSAGE"] as? String

let fn = c.value["FIRST_NAME"] as? String
let ln = c.value["LAST_NAME"] as? String

let USER_ID = c.value["ID"] as? String

if let userID = USER_ID {
if let msg = message {
if let firstName = fn {
if let lastName = ln {
let username = "\(firstName) \(lastName)"
self.addMessage(userID, text: msg, name: username)

print("Message added! \nMessage Info:")
print("User ID: \(userID)")
print("text: \(msg)")
print("Username: \(username)")
} else {
print("LN did not pass")
}
} else {
print("FN did not pass")
}
} else {
print("Msg did not pass")
}
} else {
print("User ID did not pass")
}
}
}
})

Answer

Solution: After very extensive searching and attempting, the problem still persisted that once the snapshot was converted to a snapVal (snapshot.value), the order often rearranged. My (working) solution:

for child in snapshot.children {
let child = child as! FIRDataSnapshot
 if let childVal = child.value as? [String: AnyObject] {
    let childMessage = childVal["MESSAGE"] as! String
    // more code for each child. This child might be a post of a sort, which you can access properties of in a way like I did in the line above
 }
}

Process:

  1. Loop through each child in snapshot

  2. Convert the child to a FIRDataSnapshot so it is not an element

  3. Get the value of the particular child to access properties from

  4. Add in the respective code for the child following NSDictionary principles.

Why this solution is solid

Receiving snapshots in the proper order is very simple. The issue I faced was getting data in the correct order when I got the snapshot.value. This solution fixes that because the values of each child are only accessed when looping through the children of snapshot, which is sorted. This leaves the order of children still in the control of the snapshot.

I also like the snapshot.value approach by using [String: AnyObject] because it is very close to the old functionality of Firebase implementation in Swift: Simple and very clean. I actually think that using NSDictionary in this way is really a way to save time in the long run because it is not verbose in any way.