How to find parent key using child key in firebase realtime-database?

Question

In firebase realtime-database, my project have a structure like below:

- posts
    - user_id
        - post_id
            - post_content = "..."
            - date = ...
            ...

How could i find user_id by post_id?

I have searched that before but i could not find an appropriate solution for my case. If there is any i missed out, please report me and i would be thankful for you.

I have tried to use orderByKey() and orderByChild() methods but they did not helped me to handle this problem. At the end, i was able to find the wanted user_id using a logic below:

firebase.database().ref("posts")
    .once("value", function(snapshot) {
        snapshot.forEach(function(snapshot1) {
            snapshot1.forEach(function(snapshot2) {
                if (snapshot2.toJSON().postId === "post_id") {
                    var topicID = snapshot1.key;
                    console.log(topicID);
                }
            });
        });
}, (e) => {
    console.log(e);
});

As it is seen, that is not a best way to find user_id because the method loads lots of data in the client side.

So, how can i find user_id using firebase query methods or any other method, when i only know post_id?

Answer 1

One work around can be you can save user_id in post_id node

• posts
  • user_id
    • post_id
      • post_content = "..."
      • date =...
      • user_id = #id...