根据轨道条件返回设计误差

当我张贴 session 对于rails/device,我要么得到响应, user 或者我收到一条平淡的错误消息。如何根据创建会话时出现的问题发回自定义消息?

当前代码:

class V1::SessionsController < ApiBaseController

  skip_before_action :verify_authenticity_token

    def create
      email = params[:user] && params[:user][:email]
      username = params[:user] && params[:user][:username]

      @user = User.where(email: email).first if email
      @user = User.where(username: username).first if username

      if @user&.valid_password?(params[:user] && params[:user][:password])

       @user.update_user_login_timestamp
       respond_to do |format|
         format.json { render '/users/show', status: :ok }
       end
       else
         render json: {success: false, message: "no good"}, status: 500
       end
     end

   private

  def user_params
    params.require(:user).permit(:email, :password, :username)
  end

end

我想做的是:

if username_found_but_password_doesnt_match
   render json: {error: "bad password"} status: 500
 elsif username_not_found
   render json: {error: "doesnt exist"} status: 500
end