Posted on Mar 30, 2023

Command Driven Design Pattern - ROR

In this blog we'll dive into one lesser-known design pattern but highly efficient for large scaled applications which helps the code repository to keep organised and can be easily scaled up.

Design Pattern Name: Command Driven Pattern

Usually the request from client goes to the controller which speaks to the model ( database ) and send back the view or JSON.

But in this design pattern request from controller goes to a command, and a command can be having number of actions items to perform and send the response back.

In layman terms take an example of constructing a shopping mall. the action items are:

Buy the plot.
Setting up the base.
Raising the walls.
Elevators
Painting

so all these five steps can we performed a separate file called as COMMAND.

Lets consider this scenario:

Example: On User Sign up, consider these following actions are to be performed.

User must be authenticated.
User must be sent a logged-in alert email.
User should be awarded some points.
User should receive push notification.
Audit for all the above actions.

Let's create a folder in app/ called core and file called Command.rb

class Core::Command include ActiveModel::Validations attr_accessor :token def initialize(attributes = {}) attributes.each do |name, value| if methods.include? "#{name}=".to_sym method("#{name}=".to_sym).call(value) end end end # this method can be ovveridden in other classes def run end end

Now in Lets create CreateUserCommand.rb in core folder

class Core::CreateUserCommand < Core::Command attr_reader :user_params def initialize(params) super(params) @user_params = params end def run ActiveRecord::Base.transaction do authenticate_user mailer("Account Created") award_points send_push_notification mailer("User Logged In") end # can be written in JSON builder a seprate file return { name: "Samala Sumanth", git: "https://github.com/SamalaSumanth0262"} end def authenticate_user # can be separate command for user authentication puts "User Authenticated" end def mailer(message) # can be separate command for mailer puts message end def award_points # can be written in separate command for awarding points puts "User has been awarded 10 points" end def send_push_notification # User Notification Command puts "User has been sent push notification" end end

And Finally your controller should look like this

class UsersController < ApplicationController # bypass csrf protection for all the requests made protect_from_forgery with: :null_session before_action :set_user, only: %i[ show edit update destroy ] # /users/ def create render json: ::Core::CreateUserCommand.new(user_params).run end private # Only allow a list of trusted parameters through. def user_params params.fetch(:user, {}) end end

Thats It. with this approach we have moved most of the logic into command instead of having them in fatty models.