firebase firestore check if document with property and value exists

Question

I am currently trying to verify before a user creates data in the database if the data exists. Even unter an other Document id.

Like this: User creates data, firestore rules gets all documents in collection and checks if the property name is the same as from the user provided. If yes, return unauthorized access.

At this point I have:

function checkIfCatExists(){
      return get(/databases/$(database)/documents/category/$(documents)).data.name != null;
    }

But this does not work. Do you guys have an idea? I could create a function for that but I want to do as much as possible with rules.

Answer 1

There is no way to search a collection for a specific value in security rules, as that operation wouldn't scale.

If you want to ensure unique user names, you'll have to create a collection where you use the user names as the key. You can then use the exists function in your security rules, to check if the name already exists in the collection.

Also see:

• Cloud Firestore: Enforcing Unique User Names
• Firestore security rule to check if character username already exists
• Firestore security rules - can I query for a document with specific fields?
• I want to write a rule that will don't allow add same document second time