Firebase Realtime DB: Howto index properly on key-value pair

Question

Question

I have this Firebase Realtime Database:

{      
  "groupUsers" : {
    "group1key" : {
      "user1key" : &quo         


        

Answer 1

There is no way to pre-create the indexes for such a structure. I've covered this type of structure in my answer here and here and the new Firestore documentation (which works similarly in this aspect) even has a documentation page about it.

The recommendation is to store data in a way that allows this lookup in the other direction too. With your current structure you can efficiently look up the users in a group. To also allow looking up the groups for a user, add this structure:

{      
  "usersGroups" : {
    "user1key" : {
      "group1key" : "admin",
      "group2key" : "admin"
    },
    "user2key" : {
      "group2key" : "readonly",
    },
    "user3key" : {
      "group2key" : "readwrite"
    }
  }
}