Firestore - subcollection query for a specific document

Question

Note: Querying across subcollections is not currently supported in Cloud Firestore. If you need to query data across collections, use root-level collections.

When I read the documentation for me it's not clear if it's possible to do something like this:

var listsRef = db.collection("users/user1/lists");
var query = listsRef.where("public", "==", true);

I can understand that it's not supported if I try to do this:

var listsRef = db.collection("users/{userId}/lists");
var query = listsRef.where("public", "==", true);

But I am wondering if I can query in a specific collection that comes from a specific document. In fact, what's the difference here and in a root collection?

Thanks in advance.

Your first snippet executes a query against the lists subcollection of the user1 document in the users collection. So if you have many users, each with their own lists, only the lists of user1 are queried. — Frank van Puffelen

Tom Bailey Tom Bailey · Accepted Answer · 2018-01-09T22:37:14

The SDK now supports this

Please see the other answers below...

Old answer

You can query on a subcollection as long as you know the document it belongs to. For example the following is a valid subcollection query:

const usersCollection = firestore.collection("users");
const adminDocument = usersCollection.doc("admin");
const adminsFollowersQuery = adminDocument.collection("followers").where("name", "==", "Arthur Dent");

adminsFollowersQuery.get().then((adminsFollowers) => {
  adminsFollowers.docs.forEach((adminFollower) => {
    console.log(adminFollower.get("name"));
  });
});

As you point out the following is NOT currently valid:

const allUserFollowersQuery = firestore.collection("users/{wildcard}/followers")
  .where("name", "==", "Arthur Dent");

adminsFollowersQuery.get().then((allUserFollowers) => {
  allUserFollowers.docs.forEach((follower) => {
    console.log(follower.get("name"));
  });
});

I think the documentation here is a little confusing but by "Querying across subcollections" they mean, you can query a specific subcollection, as above, but you cannot query general subcollections. At least not as a single action using the FireStore SDK.

Firestore - subcollection query for a specific document

2 Answers