Query multiple nodes for Recycler View?

Question

I have my Firebase DB setup like so,

I want to retrieve the childs pointed to by the blue arrows. They are the last messages in each chat. I want to use the values to fill a RecyclerView. However, in order to retrieve all the last messages in each chat I have to do multiple queries and the RecyclerView requires a single query. Or so it seems to be the case from what I've googled so far.

Another solution I tried was to create a ListView and fill it with a custom adapter. Then by doing multiple queries I can fill a list and use that instead of a query. However, in order to fill the list I need to make it final in the local scope of a snapshot. That doesn't work because I have two snapshots.

I have thought of simply redesigning my DB however, I can't think of a way to do it without making the DB unorganized. Any help or suggestions is greatly appreciated.

Answer 1

The only way to do this with your current data structure is, as you've already noticed, with a separate query for each node under chat .

As usual with NoSQL databases, the solution is to modify/augment the data model to make the use-case easier. In this case, I'd store the information you need directly under a new top-level node.

lastChatMessages: {
  "0hV9...Ri83": {
    ...
  },
  "IZsn...QHn2": {
    ...
  }
}

So whenever you add a new message to /chats , you also set the same information in /lastChatMessages with the same first-level child ID.

This sort of data duplication is quite common in NoSQL databases. If that's new to you, I'd recommend reading NoSQL data modeling , watching Firebase for SQL developers , and possible also Getting to know Cloud Firestore . That last one is for Cloud Firestore, but most concepts apply to many NoSQL databases.