Firebase Firestore

 Firestore is a real-time database. Which makes life easier. Firestore is completely managed, serviced and scaled automatically by google firebase. 

Some Interesting Features are:

• Real time, NoSQL cloud database (i.e. we don't use tables and columns and rows)
• We split our data up into collections and inside each of those collections we store documents which we can take as records 
• Each records has a unique identifier. 
• Each records/documents will look something like a JavaScript object with different (Key: Value) pair
• Each fields can have Strings, Arrays, Number, Time, etc...
• We could easy get the whole collections or each documents in collections. 
• We can make all database queries using Firebase SDK from frontend to communicate with our database and so we don't worry about backend code. 

Implementation:

//firebase
implementation(platform("com.google.firebase:firebase-bom:24.6.0"))
implementation("com.google.firebase:firebase-firestore-ktx")

val listener = Firebase.firestore
    .collection(COLLECTION)
    .addSnapshotListener { value, error ->
        if (error!= null){
            close(error)
        } else {
            if (value != null) {
                val list = value.toObjects<Astronaut>()
                if (list.isNotEmpty()) {
                    offer(ApiStatus.success(list))
                } else {
                    offer(ApiStatus.error("Empty List", null))
                }
            } else {
                offer(ApiStatus.error("Error", null))
                close(CancellationException())
            }
        }
    }
awaitClose { listener.remove() }