CommandServiceObject

Rails Generator for command service object.

Theory

Command Design Pattern consists of Command Object and Service Object (Executor), Command object is responsible for containing Client requests and run input validations on it to ensure that the request is valid and set default values, then Service Object applies the business logic on that command.

Implementation

Service consists of several objects { Command Object Usecase Object And Error Object (business logic error) }.

  • Command: the object that responsible for containing Client requests and run input validations it's implemented using Virtus gem and can use activerecord for validations and it's existed under commands dir.
  • Usecase: this object responsible for executing the business logic, Every usecase should execute one command type only so that command name should be the same as usecase object name, usecase object existed under 'usecases` dir.
  • Micros: Small reusable logic under the same service.
  • Externals: Simple ruby module works as a service interface whenever you wanna call any external service or even service that lives under the same project you should use it.
  • Queries: This dir is the only entry point for you to get any data form a service.
  • Listeners: An event listener that waits for an event outside the service to occur.
  • Entities: Many objects are not fundamentally defined by their attributes, but rather by a thread of continuity and identity.

Result Object

In case of successful or failure ApplicationService the responsible object for all services will return service_result object this object contain value! method containing successful call result, and errors method containing failure errors objects.

Helpers:

  • Fail: You can use fail! helper to raise business logic failures, ex: fail!('user should not have any active cards').
  • Check: To do business logic validations you can use check! helper ex: check!('user should not have any active cards') { user.active_cards.empty? }, if the given block returns false then it will raise fail! with the given message.

You can check if the result successful or not by using ok? method.

Installation

Add this line to your application's Gemfile:

gem 'command_service_object'

And then execute:

bundle

Or install it yourself as:

gem install command_service_object

Next, you need to run the generator:

rails generate service:install

Usage

$ rails g service [service_name] [usecases usecases]

Generate Service ex

$ rails g service auth login output

app/services/
├── application_service.rb
├── auth_service
│   ├ external/
│   ├── commands
│   │   └── login.rb
│   └── usecases
│       ├── login.rb
│       └── micros
├── case_base.rb
└── service_result.rb

Generate micros ex

$ rails g service:micro auth generate_jwt_token_for

app/services/
├── auth_service
│   └── usecases
│       └── micros
│           └── generate_jwt_token_for.rb

# app/services/auth_service/usecases/micros/generate_jwt_token_for.rb

module PaymentService::Usecases::Micros
  class GenerateJwtTokenFor < CaseBase
    def call
        # <Payload>
    end
  end
end

then you can edit command params

you can read Virtus gem docs for more info. 

# app/services/auth_service/commands/login.rb
# frozen_string_literal: true

module AuthService::Commands
  class Login < CommandBase
    # You can read Virtus gem doc for more info.
    # https://github.com/solnic/virtus

    # Attributes
    # attribute :REPLACE_ME, String

    # Validations
    # validates :REPLACE_ME, presence: true
  end
end

and then add your business logic

# app/services/auth_service/usecases/login.rb
# frozen_string_literal: true

module AuthService::Usecases
  class Login < CaseBase
    include CommandServiceObject::Hooks
    micros :generate_jwt_token_for
    #
    # Your business logic goes here, keep [call] method clean by using private
    # methods for Business logic.
    #
    def call
      token = generate_jwt_token_for(cmd.user)
      replace_me

      output
    end

    def output
      # return entity object
    end

    # This method will run if call method raise error
    def rollback
      # rollback logic
    end

    def allowed?
      # policies loginc for issuer
      # ex:
      #
      #   return false if issuer.role != :admin

      true
    end

    private

      def replace_me
        # [business logic]
      end
  end
end

External APIs or Services

You can wrap external apis or services under external/ dir

ex

module External
  module StripeService
    extend self

    def charge(customer:, amount:, currency:, description: nil)
      Stripe::Charge.create(
        customer:    customer.id,
        amount:      (round_up(amount, currency) * 100).to_i,
        description: description || customer.email,
        currency:    currency
      )
    end
  end
end

usage from controller

class AuthenticationController < ApplicationController
  default_service :auth_service

  def Login
    cmd    = command.new(params) # AuthService::Commands::Login.new
    result = execute(cmd)

    if result.ok?
      render json: result.value!.as_json, status: 201
    else
      render json: { message: result.error }, status: 422
    end
  end
end

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/adham90/command_service_object. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the CommandServiceObject project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.