For Firestore listeners, are security rules checked only on the initial query, or also on subsequent updates received?

Question

For example, let's say I have a Firestore security rule that uses a get() function, and my initial listener call fetches 100 documents. So that's 101 read operations. Then let's a single document is changed. On receiving the updated document, is the Firestore rule checked again, resulting in 2 reads (the document changed, and the get() function in the rules)?

Answer 1

Yes,Any time you update the dependent documents in your DB that will count as a document read.

And Every request from the Client SDK will be first routed through Security Rules no matter what change occurred . On updating the document and retrieving the document resulting in two reads.

You can also refer this document for more information which has following line which will help you

You are charged for reads that are necessary to evaluate your Cloud Firestore Security Rules.

For example, if your rules refer to three documents, but Cloud Firestore only has to read two of those documents to evaluate your rules, you will be charged for two additional reads for the dependent documents.