how to get changes in a firestore document array of object

Question

I have a collection called chats, I want to listen on the document for changes in the msg while also returning the data from the msg field, I have come up with a query but I am not getting the result I want. below is the code.

 getCurrentMsgs(chatId){
   return this.firestore.collection('chats', ref => ref.where('id', '==', chatId))
   .snapshotChanges()
    .pipe(
      map(actions => {
        return actions.map(a => {
          // eslint-disable-next-line @typescript-eslint/ban-types
          const data: Object = a.payload.doc.data();
          const id = a.payload.doc.id;
          return { id, ...data };
        }
      );
    })
  );
  }

Answer 1

The snapshot received from listeners will always contains data of that whole document. You'll have to compare existing document data and the newly received update to get the changes in array. Packages like deep-object-diff might be useful in this case.