Firebase Realtime Database validations rules not working

Question

This is my first question, so if I miss to include something please tell me, and many thanks for reading it.

I have a realtime database with this structure:

-transactions
  -uid
    -transaction1...

When adding a new transaction with these rules:

{
  "rules": {
    
    "transactions": {
      "$uid":{
        ".read": "auth != null && auth.uid == $uid",
        ".write": "auth != null && auth.uid == $uid",
      }
    }
  }
}

And this url: (I am using the REST API)

POST https://{{appName}}.firebaseio.com/transactions/{{userId}}.json?auth={{TOKEN}}

With this data:

{
    "title": "Postman Test",
    "amount": 50,
    "date": "2020-11-15",
    "category": "other"
}

It works as expected. But when I add the following validation:

{
  "rules": {
    
    "transactions": {
      "$uid":{
        ".read": "auth != null && auth.uid == $uid",
        ".write": "auth != null && auth.uid == $uid",
          
        ".validate": "newData.hasChildren(['title','amount'])",
      }
    }
  }
}

It return the following error: "error": "Permission denied"

If i put !newData.hasChildren(['title', 'amount']) instead, it works, so i assume it is not reading the fields correctly.

I should mention that when i try this rule in the firebase page, they work, so i am confused.

I have read the documentation and searched for similar errors, but i can't fix it, so any help would be really appreciated.

Thank you very much.

Answer 1

I finally could find a solution, so I would post it here in case anyone has the same problem.

When using POST in Firebase Realtime Database , it creates a new node with a new automatic index, so all i had to add was the "$id" (or any other name) field to account for that, as follows:

{
  "rules": {
    
    "transactions": {
      "$uid":{
        ".read": "auth.uid == $uid",
        ".write": "auth != null && auth.uid == $uid",
        
        "$id":{
          
          ".validate": "newData.hasChildren(['amount','category','type','date'])",
            
            "amount": {
                ".validate": "newData.isNumber() && newData.val() >= 0",
            },
            "category": {
                ".validate": "newData.isString()",
            },
            "type": {
                ".validate": "newData.isString()",
            },
            "date": {
                ".validate": "newData.isString()",
            }
            
        }
      }
    }
  }
}