ServiceBase and DryService in Rails

Welcome to the ServiceBase and DryService README! This guide will walk you through the usage and benefits of these modules in a Rails application and why we use it at Two Barrels!

Introduction

The DryService module and ServiceBase class aim to streamline service object creation in Rails by integrating dry-validation for input validation. This ensures consistency and predictability across different contexts (controllers, background jobs, tests, etc.) by validating inputs directly within the service classes.

Why Validate This Way?

Traditionally, input validation in Rails has relied on ActionController::Parameters within controllers, often neglecting validation in other contexts like background jobs or inter-service communication. By incorporating validation directly into service objects, we achieve:

• Consistent validation across different contexts
• Automatic creation of accessor methods for validated parameters
• Improved readability and maintainability of service code

How It Works

The ServiceBase class includes the DryService module, which provides validation capabilities using dry-validation. Here’s a quick rundown:

1. Define a Contract: Use the contract method to specify expected parameters and their validations.
2. Validate Parameters: The validate_params! method ensures that parameters conform to the defined contract, raising a ValidationError if they do not.
3. Implement setup and execute Methods: Child classes must define these methods to perform service-specific logic.

Example

Here’s an example service class:

module Checkout::Products
  class DomainCheckoutService < ::ServiceBase

    contract do
      params do
        required(:shopping_cart_item).value(type?: ShoppingCartItem)
        required(:contact).filled(:hash)
      end
    end

    def setup
      fail!("FQDN is required") unless fqdn.present?
      fail!("Service was not created") unless associated_service.present?
    end

    def execute
      create_or_transfer_domain
      verify_domain_transaction
      update_service_with_domain_info
    end

    private

    attr_reader :fqdn, :transfer_code, :associated_service, :domain_id

    def create_or_transfer_domain
      return initiate_transfer_domain if domain_transfer?

      create_new_domain
    end

    def create_new_domain
      domain_result = Domains::CreateDomainService.new(
        account_id: Current.account_id,
        fqdn: fqdn,
        contact_id: contact.dig(:data, :id),
        service_id: associated_service.id
      ).run!

      @domain_id = domain_result&.dig("id")
    end

    def initiate_transfer_domain
      fail!("Transfer code is required") unless transfer_code.present?

      payload = {
        "account_id": Current.account_id,
        "domains": [
          {
            "fqdn": fqdn,
            "transfer_code": transfer_code,
            "service_id": associated_service.id,
            "contact_id": contact.dig(:data, :id),
          },
        ]
      }
      domain_result = Domains::InitiateTransferService.new(payload).run!

      @domain_id = domain_result&. &.dig("id")
    end

    def verify_domain_transaction
      fail!("Transfer failed for #{fqdn}") unless domain_id
    end

    def update_service_with_domain_info
      associated_service.update!({
        data: {
          domain: {
            fqdn: fqdn,
            id: domain_id,
          }
        }
      })
    end

    def domain_transfer?
      @transfer ||= shopping_cart_item.data.dig("meta", "is_transfer") == true
    end

    def fqdn
      @fqdn ||= shopping_cart_item.data.dig("meta", "domain")
    end

    def transfer_code
      @transfer_code ||= shopping_cart_item.dig("meta", "transfer_code")
    end

    def associated_service
      @service ||= shopping_cart_item.order_item.renewable_service
    end
  end
end

Installation

Add dry-validation to your Gemfile:

ruby
Copy code
gem ‘dry-validation’
Usage
Create your service classes under app/services/ and include ServiceBase. Define your contract and implement the setup and execute methods.

Benefits

• Consistent Validation: Ensures input validation is consistent across all service calls.
• Automatic Accessors: Creates accessor methods for validated parameters, simplifying service logic.
• Clear Error Handling: Provides a structured way to handle and communicate validation errors.

Error Handling

• Custom errors can be defined within your service classes to handle specific failure scenarios:

class DocumentLockService < ServiceBase
  class DocumentLockServiceError < ServiceError; end
  class DocumentNotFoundError < DocumentLockServiceError; end

  def setup
    fail!("Document does not exist", DocumentNotFoundError) if @document.blank?
  end
end

Declaring Output

Clearly define the shape of your @result in the setup method to improve readability and predictability:

def setup
  @result = {
    name: '',
    description: '',
    price: '',
    data: {}
  }
end

Executing Services

Execute services using:

result = YourService.new(params).run!

Advanced Contract Example

You can create standalone contracts and use them within your services:

module Schemas
  module StorefrontVariant
    Create = Dry::Schema.Params do
      required(:storefront_id).filled(:string)
      required(:storefront_variant).hash do
        required(:vendor_product_id).filled(:string)
        required(:name).filled(:string)
        optional(:description).filled(:string)
      end
    end
  end
end

contract do
  params(Schemas::StorefrontVariant::Create)
end

Conclusion

By integrating dry-validation within service objects, we achieve a robust and maintainable way to handle input validation in Rails applications. This approach ensures consistent validation, clear error handling, and a predictable service structure, making your codebase more resilient and easier to work with. Happy coding! 🚀