Firebase: How many snapshot listeners is my query causing?

October 19, 2022

Firebase has a limit of 100 snapshot listeners per client. I have a Screen called "MyChats" which displays all the chats a user has and wanted to know the following:

Is my below function, which gets the data for the screen, counting as just a single listener?
Would grabbing the latest message for each chatroom (to list it in a preview, similar to Whatsapp, FB Messenger and other chat applications) affect my number of listeners?

firestore
  .collection("chats")
  .where("membersArray", "array-contains", currentUser.uid)
  .where("deletedAt", "==", null)
  .orderBy("lastMessage.date")
  .startAt(new Date())
  .onSnapshot(...);

>Solution :

Is my below function, which gets the data for the screen, counting as just a single listener?

You are calling onSnapshot() only once so that’s only 1 listener.

Would grabbing the latest message for each chatroom affect my number of listeners?

If you are referring to above code, that’s just a single query with 1 listener. If you individually add a listener for each document then that’ll be N listeners.

const col = db.collection("chats");

// 1 listener irrespective of number of documents in collection
col.onSnapshot(...)


// 3 listeners, as they are assigned separately
col.doc("1").onSnapshot(...)
col.doc("2").onSnapshot(...)
col.doc("3").onSnapshot(...)