rossme / active-record-aggregations

ActiveRecord Aggregations Playground

This repository serves as a playground for learning about Active Record Aggregations and their uses (Rails 7.0.8). It specifically focuses on the composed_of macro for representing attributes as value objects. The example below demonstrates how to use this feature.

Usage

In an ActiveRecord model, we can use composed_of to define relationships with value objects:

class Customer < ApplicationRecord
  composed_of :balance, class_name: 'Money', mapping: { balance: :amount }
  composed_of :address, mapping: { address_street: :street, address_city: :city }

  validates_with CustomerAggregations::Address, on: :create
  validates_with CustomerAggregations::Balance, on: :create
end

The validate_attributes(record) private method below returns an array composed of a boolean and a symbol. The boolean represents the validation result and the symbol represents the aggregation class name that failed validation. This allows us to use the same validator for multiple attributes.

module CustomerAggregations
  class Address < Base

    private

    def validate_attributes(record)
      [record.address.city.present? && record.address.street.present?, :address]
    end
  end
end

module CustomerAggregations
  class Base < ActiveModel::Validator

    private

    def validate(record)
      result = validate_attributes(record)
      return if result.include?(true)

      record.errors.add :base, "#{result[1]} record is invalid."
    end
  end
end

# basic validator concern

require 'rails_helper'

RSpec.describe CustomerAggregations::Base do
  describe '#validate_attributes' do
    let(:customer) { Customer.new }
    let(:balance) { Money.new(100, 'USD') }

    it 'is invalid when the address has no street' do
      customer.address = Address.new(nil, 'Ruby Town')
      customer.balance = balance

      expect(customer).to be_invalid
    end

    let(:address) { Address.new('123 Main St.', 'London') }

    it 'is valid when the address has a street and city' do
      customer.address = address
      customer.balance = balance

      expect(customer).to be_valid
    end
  end
end

Further information

ActiveRecord::Aggregations