Firebase index required but no link provided

Question

Tip: instead of creating indexes here, run queries in your code – if you're missing any indexes, you'll see errors with links to create them. Learn more

I'm getting an error no matching index found without the usual direct link to create the index required.

My database is structured as follows:

answers (collection)
  - $docId (document)
      - $refId (collection)
          - $docId (document)
              - created_at (timestamp)
              - type (string)

My query is:

firebase.firestore()
 
 .collection('answers')
 .doc('abcdHajM930Gabcd')
 .collection('abcdetIo25xYqAabcd')
 .orderBy("created_at", "desc")
 .limit(5)
 .where("type", "==", "3")

I've tried all combinations of indexes I could think of (screenshot below), What am I doing wrong?

collection	field	type
answers	created_at: DESC	type: ARRAY
answers	created_at: DESC	type: ARRAY
answers	created_at: DESC	type: ASC
answers	created_at: DESC	type: ASC
answers	type: ASC	created_at: DESC
answers	type: ASC	created_at: DESC

Answer 1

Update: The issue seems to be fixed and Javascript client SDK now returns the index creation link.

---

I'm not totally sure if that's intended by the Firebase JS SDK or no, but if you try running your query in a Cloud Function (just use the emulator) then it should throw an error containing the link to create the index.

export const getIndexLink = functions.https.onRequest(async (request, response) => {
    //   functions.logger.info("Hello logs!", {structuredData: true});
    try {
        const snap = await admin.firestore().collection('answers')
            .doc('abcdHajM930Gabcd')
            .collection('abcdetIo25xYqAabcd')
            .where("type", "==", "3")
            .orderBy("created_at", "desc")
            .limit(5).get()
        console.log(snap.size)
        response.send("Hello from Firebase!" + snap.size);
    } catch (error) {
        console.log(error)
        response.send(error.message)
    }
});

I tried copying your query and created an index using the URL and the index turns out to be:

Your fields that your are using are not a part of documents of "answers" collection. Now if you change the sub-collection name, it'll require another index. What does your Firestore structure look like? I'd recommend restructuring it a bit and get a same sub-collection name and create an index with collectionGroup scope.