How to add values to Firebase Firestore without overwriting?

Question

I have two Activities, I am adding data to Firestore from these two activities individually. But, whenever I add second activity data to Firestore, it is overwriting the fir

Answer 1

There are two ways in which you can achieve this. First one would be to use a Map:

Map map = new HashMap<>();
map.put("yourProperty", "yourValue");
firebaseFirestore.collection("Users").document(user_id).update(map);

As you can see, I have used update() method instead of set() method.

The second approach would be to use an object of your model class like this:

YourModelClass yourModelClass = new YourModelClass();
yourModelClass.setProperty("yourValue");
firebaseFirestore.collection("Users").document(user_id)
    .set(yourModelClass, SetOptions.mergeFields("yourProperty"));

As you can see, I have used the set() method but I have passed as the second argument SetOptions.mergeFields("yourProperty"), which means that we do an update only on a specific field.