can't create new children in firebase database aftter setting the rules - firebase

Question

I am using firebase database in my app. I have set the rules to allow normal users to create new childs in the node but I found that it's refused.
this is the writing rules of the node :
".write":"auth.uid == \"DFhNb28506Y345CpJ3Ye7DQNn713\" || ((newData.exists() && !data.exists()) || auth.token.email == data.child(\"userEmail\").val())",
I think that newData.exists() && !data.exists() should allow users to write in the database but this doesn't happened
this is the rules of the users node :
"users":{
".write":"auth.uid == \"DFhNb28506Y345CpJ3Ye7DQNn713\" || ((newData.exists() && data.child(\"userEmail\").val() != null) || auth.token.email == data.child(\"userEmail\").val())",
".read": "auth != null"
}
The database strucutre is like that :
-users
-user1
-userName, userEmail ....
-user2
-userName, userEmail .....
when a new user sign up in the app he should be allowed to push his data in the database
this is the database structre :

Answer 1

Ok, I think you're creating extra validation steps that aren't needed.
First
With ".read": "auth != null" on your users root, each user is able to access other user's data, so we should address the access for each user individually.
Second
If you just want to allow users that are authenticated to write and read its own contents, you can remove these extra ((newData.exists() && !data.exists()) and auth.token.email == data.child(\"userEmail\").val()) steps.
Tip: this ((newData.exists() && !data.exists()) comparison means exactly: Write here if you're sending anything but there should be nothing written in this requested "path". You should reflect on the need of this, as I don't know your exact use cases.
Also, I would guess the hardcoded UID you're requesting is of an Admin you've created - I wouldn't recommend this, please read more about user roles on this answer.
To clarify, I think your rules structure should be something like this:
{
"rules": {
".write":"auth.uid == \"DFhNb28506Y345CpJ3Ye7DQNn713\",
".read": "auth.uid == \"DFhNb28506Y345CpJ3Ye7DQNn713\",
"users": {
"$uid": {
".read": "$uid === auth.uid",
".write": "$uid === auth.uid"
}
}
}
}