Add another data to the firebase database

Question

In my web app, I want to create a classroom and add the data to my firebase database.

var fbclass = firebase.database().ref().child('Classes');

function classcreation(q) {

  var usuid = generateId();
  var myClasses={};

  myClasses.TheClass = document.getElementById('classroomName').value;
  myClasses.Teacher = user.displayName;
  myClasses.TeacherEmail = user.email;
  myClasses.ClassID = usuid;
  fbclass.child(user.uid).set(myClasses);
  }

function generateId(){
return 'xxxx-xxxx-xxxx'.replace(/[x]/g, function(){
  return (Math.random() * 9 | 0 ).toString();
  })
}

After submitting the button it will then store the data to the firebase

but the problem is, if I create another classroom with the same user, it will just update the TheClass[classname] and not create another classroom.

What's wrong with my code? What did I miss?

Renaud Tarnec · Accepted Answer · 2018-09-20T08:58:31.847

1

By using the set() method you are writing the data at the fbclass.child(user.uid) location (i.e. reference), see the doc.

Since your location is based on user.uid you are using the same location again and again for a given user: hence the overwrite you encounter (since set() "overwrites any data at this location and all child locations").

You should generate a unique key, each time you write a new classroom for the same user. For that you should use the push() method (doc) which "generates a new child location using a unique key", as follows:

var newClassroomRef = fbclass.child(user.uid).push(
  {
    'Class_Id': '....',
    'Teacher': '....'
  }
);

The following would also work:

var newClassroomRef = fbclass.child(user.uid).push();
newClassroomRef.set({
  'Class_Id': '....',
  'Teacher': '....'
});

Note that this will create an extra level in your node tree, under the user.uid node;

- Classes
    - yo9HQ.......  <- user.uid
        - 6trQEd.......  <- classroom uid
           - Teacher: .....
           - .....: .....
        - PKH6fd.......  <- classroom uid
           - Teacher: .....
           - .....: .....

edited Sep 20 '18 at 08:58

answered Sep 20 '18 at 08:48

Renaud Tarnec

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How do I retrieve the data? var getClassInfo = firebase.database().ref().child('Classes'+ user.uid + '/'); getClassInfo.on('value', gotData,errData); function gotData(data) { //console.log(data.val()); var Classes = data.val() var keys = Object.keys(Classes); console.log(keys); for (var i =0; i < keys.length; i ++){ var k = keys[i]; var TheClass = Classes[k].TheClass; console.log(TheClass); } } function errData(err) { console.log('Error!'); console.log(err); } – Dodong Advices Sep 20 '18 at 15:06
I would suggest you create a new question as this is different from your initial question and secondly it is really not easy to read code within comments!! – Renaud Tarnec Sep 20 '18 at 15:08
Okay, I will put the link here – Dodong Advices Sep 20 '18 at 15:10
1

[link](https://stackoverflow.com/questions/52428450/how-can-i-get-the-reference-of-the-push-in-firebase-database) @Renaud Tarnec here's the link ;) – Dodong Advices Sep 20 '18 at 15:22
I was about to reply to your answer but it seems that it was deleted – Dodong Advices Sep 20 '18 at 15:36
It should be ok now – Renaud Tarnec Sep 20 '18 at 15:42
Are u still there, mr. renaud? – Dodong Advices Sep 21 '18 at 15:10

score 0 · Answer 2 · answered Sep 20 '18 at 09:00

Here are a few pointers that'll be handy.

All keys are unique. You cannot have two indices of same key. Having said that, you are assigning a key as user.uid which will always be the same. Essentially, you are updating the value present at the key.
Here, I am assuming you want to make keys based on the uid of the user using the database. So, using set will only store your data, which means if you give it a new uid, it'll wipe off the data in your Classes key and set it with your new user.uid key that you have provided. If you want to append the new key, you'll need ti use the method update instead of set. It'll update your Classes key with the new user.uid key which means that you'll appending data to your Classes object. Something on the lines of - fbclass.child(newUserID).update(myClasses);

Hope it helps :))

Add another data to the firebase database

2 Answers2