Java, Firebase: How to search values of an unknown parent

Question

I have a database in firebase which sort of looks like this:

-Messages
  -randomGenKey
    -receiverUid:string1
    -senderUid:string2

I am trying to search if string1 and string2 are a specific value lets say "user1" and "user2", respectively. I am unsure of how I can accomplish this. I know I can get to Messages by simply doing mMessagesRef = FirebaseDatabase.getInstance().getReference().child("messages"); But get stuck after that because randomGenKey is unknown when I am searching.

As Frank van Puffelen explained in his answer they key is duplicate data. An effective way I have found to create the keys for each chat is to clean both users email's and then join them. Remove dots, you can leave the at symbol. And add them together to create a unique key. You can safely do it unique by adding both strings alphabetically. By example: "jhon@gmailDOTcom - user1@mailDOTcom" — cutiko, Aug 13 '17 at 16:14

score 2 · Answer 1 · answered Aug 13 '17 at 14:33

As @creativecreatorormaybenot said, you can you a query to filter on either senderUid or receiverUid. But a Firebase Database query can only filter on one property, so you cannot use it to filter on both properties. You may be able to combine the two values into a single property and filter on that. For more into on this and other ways to filter, see my answer here: http://stackoverflow.com/questions/26700924/query-based-on-multiple-where-clauses-in-firebase

But since it seems like you're creating a messaging application, I'd also consider an alternative data structure. If your users are having 1:1 conversations, I'd recommend looking at a data structure that models each conversation as a node in the tree. So instead of having one long list of messages between all of the users of your app (very much a SQL model), model it as multiple (much smaller) conversations:

-Messages
  -keyOfRoomOne
    -message1
    -message2
  -keyOfRoom2
    -message1
    -message2

And then also keep a list of all the rooms for each user:

-Users
  -Uid1
    -keyOfRoomOne
    -keyOfRoomTwo
  -Uid2
    -keyOfRoomOne
  -Uid3
    -keyOfRoomTwo

With this structure you look up the room ID when the chat starts, which is much less frequently than for each message.

Alternatively you can use a room name that reflects the users in it and not even need the lookup. For more on that, see http://stackoverflow.com/questions/33540479/best-way-to-manage-chat-channels-in-firebase

score 1 · Answer 2 · answered Aug 13 '17 at 13:33

FirebaseDatabase.getInstance().getReference("messages").orderByChild("receiverUid").equalTo("user1")

You cannot use two queries, so this is as far as you get. You will be able to check if senderUid equals user2 on the client side by going through all the result objects. Find more on this here.

Java, Firebase: How to search values of an unknown parent

2 Answers2