How to get all posts where current user has not commented yet using firebase realtime database?

Question

My use case is to fetch all posts which is not already commented by current user.

I want to achieve this with single query but my current approach is not working.

DB structure:

posts: {
   post1:{
      content: "Lorem Ipsum"
      comments: {
         uid1: true,
         uid2: true
                }
          }
         }

My query looks like this:

   val postsRef = FirebaseDatabase.getInstance().reference.child("posts")
            .orderByChild("comments/{uid}")
            .equalTo(null)

Above query an index, but my current index is one dynamic value which firebase doesn't allow.

"posts" : {
"$postId": {
  "comments": {
      ".indexOn" : ".value"
  }
}

}

I'm stuck here, it would be helpful if anyone guide me to achieve this. Thanks

Answer 1

Firebase database queries can only check for the presence of a certain value, not for the absence of it.

So you can either add each user ID to each post and then remove them when they comment, or (more likely) you will have to implement the logic in your application without a database query: just load all posts and remove the ones where you then find that this user already commented.