Firebase Firestore update data

Question

I am using firebase firestore to create my website, this is one sample of document:

As you can see, I have a field call commentList and its type is array , now I want to push more document in the the array and this is how I did (and it not work out, of course):

const {db} = require('../util/admin');

exports.add__comment = (req, res, next) => {
  const {comment, displayName, uid} = req.body;
  const {id} = req.params;

  return db
    .collection('instagram__posts')
    .doc(id)
    .set(
      {
        commentList: [
          {comment, uid, displayName, createAt: new Date().toISOString()},
        ],
      },
      {merge: true}
    )
    .then((doc) => {
      return res.status(200).json({message: 'comment created', doc});
    })
    .catch((err) => {
      res.status(500).json({err});
      console.log(err);
    });
};

Instead of adding more document to commentList , it replace all current documents with new data. Please help me and pardon me for my bad English. Once again thank you so much and have a good day.

Answer 1

Try push element to direct path.

firebase.firestore()
  .collection('instagram__posts')
  .doc(id)
  .collection('commentList')
  .add({comment, uid, displayName, createAt: new Date().toISOString()})

Show details here: https://cloud.google.com/firestore/docs/manage-data/add-data#update-data

Answer 2

If you want to add another element to a list type field, use update() and FieldValue.arrayUnion() , as shown in the documentation .

  db
    .collection('instagram__posts')
    .doc(id)
    .update({
      commentList: firebase.firestore.FieldValue.arrayUnion({comment, uid, displayName, createAt: new Date().toISOString()})
    })