Firebase database rule - Check for initial child values - firebase-realtime-database

Question

A user should only be created if he has the correct children with correct initial values.
The following code works but it prevents me to change the values like health after the user was created.
How can I check only for the initial child values?
{
"rules": {
".read": true,
".write": false,
"users": {
// Only allow writes in users
".write": true,
"$user": {
// Check if new user has the correct children
".validate": "newData.hasChildren(['userID', 'deviceModel', 'health', 'age', 'playername', 'score', 'clickedby', 'timestamp'])
// Check if new user has a health of 10
&& newData.child('health').val() == '10'
// Check if new user has an age of 0
&& newData.child('age').val() == '0'
// Check if new user has a score of 0
&& newData.child('score').val() == '0'
// Check if new user has a timestamp which is not a future value
&& newData.child('timestamp').val() <= now"
}
}
}
}
Update: The rules of Frank van Puffelen work perfectly
Here are my updated rules:
{
"rules": {
".read": true,
".write": false,
"users": {
// Only allow writes in users
".write": true,
"$user": {
// Check if new user has the correct children
".validate": "data.exists() || (
newData.hasChildren(['userID', 'deviceModel', 'health', 'age', 'playername', 'score', 'clickedby', 'timestamp'])
// Check if new user has a health of 10
&& newData.child('health').val() == 10
// Check if new user has an age of 0
&& newData.child('age').val() == 0
// Check if new user has a score of 0
&& newData.child('score').val() == 0
// Check if new user has a timestamp which is not a future value
&& newData.child('timestamp').val() <= now) "
}
}
}
}

Answer 1

If you only want to check for new data, you can use data.exist(). For example:
".validate": "data.exists() || (
newData.hasChildren(['userID', 'deviceModel', 'health', 'age', 'playername', 'score', 'clickedby', 'timestamp'])
// Check if new user has a health of 10
&& newData.child('health').val() == '10'
// Check if new user has an age of 0
&& newData.child('age').val() == '0'
// Check if new user has a score of 0
&& newData.child('score').val() == '0'
// Check if new user has a timestamp which is not a future value
&& newData.child('timestamp').val() <= now
)"
Unrelated: I'd consider storing numeric values in numbers, instead of in string values as you do now. So that'd be newData.child('health').val() == 10, etc.
Btw: kudos on writing such beautiful security rules early on in development. 👍