JSON structuring a groupchat - json

Question

I'm going to implement a groupchat into my app by using Firebase. I were thinking of 2 different structures of saving data in JSON.
First structure:
Second structure:
I would like to achieve a fast query and i would like it to parse a small amount of data each time. What structure should i go for and are there maybe a better alternative then these 2?

Answer 1

The first solution is clearly not viable, as you would have a hard time finding all messages belonging to a given group.
The second solution is ok if every time you will query a given group's node, you are going to need also all of its messages, which is probably not what you want.
It is hard, of course, to advise on data structure without more info on your use-case, the queries you are going to make, etc., but a rather standard approach would be:
{
"users": {
"$userId"": {
// user data
}
},
"groups": {
"$groupId": {
// group data
}
},
"group_users": {
"$groupId": {
"$userId": true
// separation of list of users from the group is useful
// if you are going to query the group node not needing its full list of users
}
},
"group_messages": {
"$groupId": {
"$messageId": {
// message data
}
}
}
}