DatabaseActivity.kt

    fun changeQuery() {
        val newQuery = mBaseQuery
            .orderByChild("timestamp")
            .limitToLast(100)

        // Make new options
        val newOptions = FirebaseRecyclerOptions.Builder<Post>()
            .setQuery(newQuery, Post::class.java)
            .build()

        // Change options of adapter.
        mAdapter.updateOptions(newOptions)
    }