How to get the value of a key in firebase - iOS - ios

Question

so this is an image of my JSON tree:
my JSON TREE
Question:
I wanted to know how can I check if the username, let's say, sean exists in the usernames. I currently have no idea on how to implement this.
What I've tried:
The key of usernames child is "theUsernameOf-userUID", and that causes the problem as userUID is dynamic and different from each user (from firebase auth), therefore I can't use:
.queryOrderedByChild("theUsernameOf-userUID").queryEqual(toValue: self.usernameTextBox.text!)
The key of usernames child can't be static like theUsername as it would only be able to have 1 value / not able to generate more node.
Thank you so much, sorry if I didn't explain clearly enough.

Answer 1

I would like to modify your DB structure as current one is not the correct to perform this query.
It should be like below:
Always use auto incremented keys for queries. Here usernames -> autoGeneratedKey -> yourData (Dictionary - Key-Value pair) Now you can easily check the existence of any key.
let ref = defaultDB.reference.child("usernames")
ref.queryOrdered(byChild: "username").queryEqual(toValue: "sean").observeSingleEvent(of: DataEventType.value) { (snapshot) in
if snapshot.exists() {
print("exists")
}
else {
print("doesn't exist")
}
}
Output: exists
This is the correct way to do so. Just checking for snapshot.exists() will do the job for you.

Answer 2

When you observe any reference in firebase, you get a DataSnapshot in return. The snapshot has a children enumerator property on which you can enumerate each child. Each of the child will be another DataSnapshot. Now, each snapshot has key and value. You want the user name? It's in the value property:
let databaseRef = Database.database().reference(withPath: "usernames")
databaseRef.observe(.value) { (snapshot) in
snapshot.children.forEach({ (child) in
if let child = child as? DataSnapshot, let value = child.value {
print(value) //"Sean", "Yuh"
// here you can check for your desired user
}
})
}

Answer 3

Here is how you can do it
Set the database reference to the usernames node. For example db.ref.child("usernames")
Now parse the snapshot using for loop
let usernames = snapshot.value as! NSDictionary
Now the for loop
for username in usernames{
if username.value == "Sean"{
// do whatever you want here
}
}

Answer 4

You could also:
Make a firebase call to usernames and make that:
let usernames = snapshot.value as? [String: AnyObject],
then all you have to do is something like
if let keyExists = usernames[YOURUSERNAMECHECKSTRING] {
//It's true
}
Just another way of looking at it.

Answer 5

Try This code will Help you you dont need to change your firebase structure
In Swift
Database.database().reference(withPath: "users").queryOrdered(byChild: "usernames").queryEqual(toValue: "yourUserName").observe(.value)
{ (snapshot:DataSnapshot) in
if snapshot.valueInExportFormat() is NSDictionary
{
// User is exits
}
else
{
}
}
In Objective c
[[[[[FIRDatabase database] referenceWithPath:#"users"] queryOrderedByChild:#"usernames"] queryEqualToValue:#"your User Name"] observeSingleEventOfType:FIRDataEventTypeValue withBlock:^(FIRDataSnapshot * _Nonnull snapshot)
{
if ([snapshot.valueInExportFormat isKindOfClass:[NSDictionary class]])
{
// User is exits
}
else
{
}
}];