Firestore query with subcollection reference from parent document-CodePudding

My Firestore database structure looks like this (as shown in image)

I have a users collection which has a posts sub-collection.

I want to fetch(query)all the posts by country(field of parent collection).

Is there any solution without any duplication of fields.

My code is below:

 val query: Query =
            postsRef
                .whereEqualTo("country", "USA"). // field from parent document
                .orderBy("createdAt", Query.Direction.DESCENDING)
                .limit(20)

CodePudding user response：

There is no way you can filter documents in a sub-collection based on the field that exists in the parent document. The best option that you have is to add the country field inside each post and use a collection group query like this:

val query = db.collectionGroup("posts")
                .whereEqualTo("country", "USA")
                .orderBy("createdAt", Query.Direction.DESCENDING)
                .limit(20)

In this way, you'll be able to get only the post from the USA. If you however need to query collections in Firestore under a certain path, please check the following article:

How to query collections in Firestore under a certain path?

P.S. Please also don't forget to create an index.

CodePudding user response：

You'll have to first query users in that country and then fetch their posts or alternatively store the country in post document as you've mentioned in your question.