todos_controller.rb

  def get_all
    @todos = Todo.all
    render json: @todos
  end

  def create
    @todo = Todo.create(todo_params)

    respond_to do |format|
      format.json do
        if @todo.save
          render :json => @todo
        else
          render :json => { :errors => @todo.errors.messages }, :status => 422
        end
      end
    end
  end

https://github.com/rubydonkey/flux-todomvc-rails-51/blob/35af561f3ea8560c63c685aa416cc65538fdfbfd/app/controllers/todos_controller.rb#L11