Firebase realtime:How to update particular value of child in Firebase Database javascript

Question

I want to update isseen value to true when the sender is equal to "5" in below code. How can I update value of issen to true . My database structer is as below:

Chats
-LvuhnORi1ugp8U2Ajdq
isseen: "false"
message: "hi"
receiver: "OX0pReHXfXUTq1XnOnTSX7moiGp2"
sender: "5"
time: "16:23:22 12/12/2019"

-Lvuw34ZiXwD6UfWWeNm
isseen: "false"
message: "hi"
receiver: "OX0pReHXfXUTq1XnOnTSX7moiGp2"
sender: "7"
time: "17:17:22 12/12/2019"

i try this code but she only update one value of the first instance in my chat table and me i want to update the value of isseen to true when the sender equal to 5

  SetSeen = ()=>{

    var db = firebase.database();
    var currentUser = firebase.auth().currentUser|| '';
    var query=   db.ref("Chats/"+currentUser.uid).orderByChild("sender").equalTo(this.props.inBox.inBox|| '');
query.once("child_added", function(snapshot) {
  snapshot.ref.update({isseen: "true" })
});
  }

can somebody help me

Answer 1

Change this:

    var query=   db.ref("Chats/"+currentUser.uid).orderByChild("sender").equalTo(this.props.inBox.inBox|| '');

into this:

    var query=   db.ref("Chats").orderByChild("sender").equalTo("5");

Add reference at node Chats then orderByChild will be able to access the attribute sender , and you can use equalTo to retrieve the data that you want

Answer 2

The reason your code only works for the first instance in your chat table is because you subscribe to the child_added event only once:

query.once("child_added", function(snapshot) {

Changing this to on(...) will re-trigger the function for each matching result.

query.on("child_added", function(snapshot) {

If possible, I would change your code so that the update to each isseen value is atomic (all-or-nothing) and make use of promises to track any errors. This can be achieved using the following code:

SetSeen = () => {
    const senderId = this.props.inBox.inBox;
    const currentUser = firebase.auth().currentUser;

    // fail-fast error handling
    if (!senderId) {
      return Promise.reject(new Error('Sender required'));
    } else if (!currentUser) {
      return Promise.reject(new Error('User required'));
    }

    // prepare query
    var db = firebase.database();
    var query = db.ref("Chats/"+currentUser.uid).orderByChild("sender").equalTo(senderId);

    return query.once("value")
      .then(queryResults => {
        if (!queryResults.hasChildren()) {
          return; // no results, nothing to update
        }

        var pendingUpdates = {};

        // add each value to be updated
        queryResults.forEach((chatSnapshot) => {
          pendingUpdates[chatSnapshot.key + "/isseen"] = "true";
        });

        // commit changes
        return queryResults.ref.update(pendingUpdates);
      });
}