Update Firebase Realtime Data Base Specific Value in an Object

Question

I am learning Flutter with Firebase. I have some dummy data in Firebase Realtime Data base as:

{
  "postsnode": {
    "posts": [
      {
        "postId": "u1",
        "postName": "p1"
      }
    ]
  },

  "usersnode": {
    "users": [
      {
        "userId": "u1",
        "userName": "bla bla 1"
      },
       {
        "userId": "u2",
        "userName": "bla bla 2"
      }
    ]
  }
}

The screen shot of the console database structure is:

I have successfully performed a query on my usersnode object to get the specific users:

void queryDB(BuildContext context) async {
    AppUtil.showLoader(context: context);
    FirebaseDatabase.instance.ref().child('usersnode/users').orderByChild('userId').equalTo("u1").get().then((snapshot) {
      if (snapshot.exists) {
        print("user:::" + snapshot.value.toString());
        final jsonResponse = json.encode(snapshot.value);
        List<dynamic> list = json.decode(jsonResponse);

        List<Users> users = [];
        list.forEach((element) {
          Users usersModel = Users.fromJson(element);
          users.add(usersModel);
        });

        users.forEach((element) {
          debugPrint("UseX:::" + element.userName);
        });
      } else {
        print('No data available.1');
      }
      AppUtil.dismissLoader(context: context);
      // }).onError((error, stackTrace) {
      //   print('No data available.2');
      //   AppUtil.dismissLoader(context: context);
    });
  }

I just want to update my specific object suppose the users object with the userId=u1 only! Can somebody help me getting this, update using the query! or I'm doing the wrong way!

Actually I just simple want to update the object based on some condition:

Update Users -> where userId=u1

Thanks in Advance!

Answer 1

You're starting with a very flimsy foundation to your database if you go down the route you're taking. A proper schema would look like this:

{
  "posts": {
      "$postID": {
          "postName": "Some Name"
          // ...
      }
  }

  "users": {
    "$userID": {
        "userName": "Some Username"
    }
  }
}

You would be wise to avoid arrays entirely when using firebase database. This isn't a firebase standard, it's a NoSQL practice.

In short, NoSQL databases use key value pairs to structure data. Since you won't have any two users with the same ids, nor two posts with the same ids, using key-value pairs in your database let you easily accomplish what you're trying to do by design.

I just want to update my specific object suppose the users object with the userId=u1 only! Can somebody help me getting this, update using the query! or I'm doing the wrong way!

The way to do this in the user nodes is as simple as this:

String userID = "$userID"; // where $userID is your targeted user
String newUserName = "$newUsername"; // this is the new data you're trying to change

DatabaseReference userRef = FirebaseDatabase.instance.ref().child('users').child(userID);
userRef.update({
    "userName": newUserName,
    "timestamp": ServerValue.timestamp,
});

I have successfully performed a query on my usersnode object to get the specific users:

Obviously your old implementation won't work when you update your schema to be key-value paired. But that's a good thing because now you can do proper queries which you can then convert into arrays in the app. You would effectively parse through the DatabaseSnapshot value, which is a Map where the keys are the userIDS and the values are corresponding data.

The way you would load the users into your app with is as follows:

DatabaseReference usersRef = FirebaseDatabase.instance.ref().child('users');
usersRef.orderByChild("userName").once(DatabaseEventType.value).then((DatabaseEvent databaseEvent) {
  // (You should update to the latest package which has breaking changes like this you need to adjust to)
  // First get the snapshot from the new DatabaseEvent object
  DataSnapshot snapshot = databaseEvent.snapshot;
  // Convert the value into a map you can parse through
  Object? snapshotValue = snapshot.value;
  Map<dynamic, dynamic> valueMap = snapshotValue is Map<dynamic, dynamic> ? snapshotValue : {};
  // Print the results for debugging
  if(valueMap.isEmpty) {
    debugPrint("No users found");
  } else {
    debugPrint("${valueMap.length} user${valueMap.length == 1 ? '' : 's'} found");
  }
  // Loop through the keys of this map (which are the userIDS)
  List<Users> users = [];
  for(String userID in valueMap.keys) {
    Users userModel = Users.fromJson(valueMap[userID]);
    users.add(usersModel);
    debugPrint("UseX:::" + userModel.userName);
  }
  AppUtil.dismissLoader(context: context);
});

Lastly, if you allow users to create posts, you might want to consider adding the following node to your schema in addition to just "posts":

"user_posts" {
    "$userID": {
        "$postID": POST_OBJECT,
        // ...
    }
}

Then when you want to load the posts created by the user, rather than only being able to query the "posts" node for posts created by the user (which you'll have a limited querying ability), you query the posts under this specific user's posts (by timestamp for example).

If you do it this way, you'd store a copy of the same object under the user's posts node and posts' node.

You seem new to firebase and have a limited understanding of how the database works. It can get very messy very fast and the most important thing to do is understand how you're going to use the data, how it's going to be queried, and most importantly, how you want to be able to sort it (by alphabetical order, by ranking, by number of likes, by date created, etc.).

Understanding these concepts now is very important because it's directly tied to your database security rules as well (which you wouldn't be able to protect with the way you were doing it before).

My advice would be to look up a quick start guide on NoSQL databases (maybe just the firebase documentation starting guide), look at the firebase database security rules guide, understand what fanning out data is, and then start looking into cloud functions so you can do useful things when data is created, updated, or deleted.

It's very easy to neglect this stuff early on while only focusing only on the app, but this is equally important despite not being something your end user would spend a second thinking about. Without a solid database, you'll run into endless issues in the future.

Good luck :)

Answer 2

Welcome to Flutter Firebase!

First, you should probably change your data structure. There's no need to have a random incremental ID for users. You can use their unique ID as the key for the object:

{
  "posts": {}
  ...
  "users": {
    "u1": {
      "userName": "bla bla 1"
    },
    "u2": {
      "userName": "bla bla 2"
    }
  }
}

Then, you can do this:

final String userId = 'u1'; 
final userDoc = FirebaseDatabase.instance.reference().child('users/$userId');

If you're planning on storing a lot of data in posts or users, I highly recommend that you check Cloud Firestore. It offers better structure and more advanced data types.