rb:dry-rb-patterns

dry-rb Patterns

Functional programming tools for Ruby with dry-rb.

Overview

dry-rb provides type-safe, composable tools for Ruby:

Gem	Purpose	Use Case
dry-validation	Schema validation	Params, forms, contracts
dry-types	Type constraints	Attribute typing
dry-struct	Immutable value objects	Domain models
dry-monads	Result/Maybe monads	Service composition
dry-transaction	Business transaction DSL	Operation pipelines
dry-system	Dependency injection	Component architecture

dry-validation

Schema-based validation for params and forms.

Basic Contract

require 'dry-validation'

class UserContract < Dry::Validation::Contract
  params do
    required(:name).filled(:string, min_size?: 3)
    required(:email).filled(:string, format?: /@/)
    optional(:age).maybe(:integer, gteq?: 0)
  end
  
  rule(:email) do
    key.failure('has invalid format') unless value.include?('@')
  end
end

# Usage
contract = UserContract.new
result = contract.call(name: 'John', email: '[email protected]')

if result.success?
  result.to_h  # { name: 'John', email: '[email protected]' }
else
  result.errors.to_h  # { email: ['has invalid format'] }
end

Rails Integration

# app/contracts/application_contract.rb
class ApplicationContract < Dry::Validation::Contract
  config.messages.backend = :i18n
  config.messages.load_paths << Rails.root.join('config/locales/dry_validation.en.yml')
end

# app/controllers/users_controller.rb
class UsersController < ApplicationController
  def create
    contract = UserContract.new
    result = contract.call(user_params)
    
    if result.success?
      User.create!(result.to_h)
    else
      render json: { errors: result.errors.to_h }, status: :unprocessable_entity
    end
  end
end

Validation Rules

class OrderContract < Dry::Validation::Contract
  params do
    required(:items).array(:hash) do
      required(:product_id).filled(:integer)
      required(:quantity).filled(:integer, gt?: 0)
    end
    required(:shipping_address).hash do
      required(:street).filled(:string)
      required(:city).filled(:string)
    end
  end
  
  # Custom rule
  rule(:items) do
    if value.empty?
      key.failure('must have at least one item')
    end
  end
  
  # Cross-field validation
  rule(:shipping_address) do
    unless valid_zip?(value[:zip])
      key(:shipping_address)[:zip].failure('is invalid')
    end
  end
end