Firestore rules for not existing documents

Question

Below code works if I have collection (in this case suppliers)

function isNotRestrictedinSuppliers(){
  let value=3;
  let suppliers=get(/databases/$(database)/documents/users/$(request.auth.uid)/settings/suppliers);
  return suppliers.data.suppliers_array.size() < value;
  //return true;
}
 match /suppliers/{document=**}{        
    allow read,update, delete: if isSignedIn() && isValidUser();
    //above is the same like allow write;
    allow create: if isSignedIn() && isValidUser() && (isPremium() || isNotRestrictedinSuppliers());  
}
match /suppliers/{supplier}{        
    allow read,update, delete: if isSignedIn() && isValidUser();
    //above is the same like allow write;
    allow create: if isSignedIn() && isValidUser() && (isPremium() || isNotRestrictedinSuppliers());  
}

Unfortunately, if there is no collection "suppliers" it doesn't work. What I want to do is restrict creation of suppliers but create if no supplier exists

Answer 1

Firebase Security Rules won't allow users to create if/else conditions. So basically you need to create another function to check if supplier documents exist and return true if it doesn't exist

function notExists(){
  let suppliers=exists(/databases/$(database)/documents/users/$(request.auth.uid)/settings/suppliers);
  return !suppliers
}

This would cost one additional read per security check