Firebase Realtime Database - Write if user is not in the User ID list OR if it is then if the newData.Val() is less than the data.Val()

Question

I want to

• if a user is not in the userID list to let him write his time( this only happens the first time - regardless his score)
• after that if his new time is less than his current time let him write to the database.

is there a way to do this? Can anyone help me ?

Unfortunately i cannot make it work. I have only succeed to the part to check the old value and the new value. This works But ONLY this if the user is ALREADY registered in the database.

I also tried to add the !data.exists but it is not working .

Below my rules

{
  "rules": {
    ".read": true,
      "Users" : {
           "3X3": {
             "$userID": {
               ".write": "data.child('time').val() > newData.child('time').val()"
             }
         }
      }
  }
}

Answer 1

I think you're looking for:

{
  "rules": {
    ".read": true,
      "Users" : {
           "3X3": {
             "$userID": {
               ".write": "
                 !data.exists() || // 👈
                 data.child('time').val() > newData.child('time').val()
               "
             }
         }
      }
  }
}

Also see the Firebase documentation on new vs existing data in security rules.