Delegation-based implementation of Rails FormObjects

form_object.rb

class AdminUsers::RegistrationForm
  include ActiveModel::Model
  attr_accessor :object

  validates :first_name, :last_name, :email, presence: true

  delegate :first_name, :first_name=,
           :last_name, :last_name=,
           :email, :email=,
           :password, :password=,
           :persisted?, to: :object

  def initialize(params, object = AdminUser.new)
    @object = object
    assign_attributes(params)
  end

  def save
    valid? && object.save
  end
end


# Tests

require 'rails_helper'

RSpec.describe 'RegistrationForm', type: :model do
  context 'if admin_user is not persisted' do
    let(:params) { { first_name: 'firsty', last_name: 'lasty', email: '[email protected]', password: 'foo2#passwo' } }

    it 'saves if valid' do
      @form = AdminUsers::RegistrationForm.new(params)
      expect { @form.save }.to change(AdminUser, :count).by(1)
    end

    it 'fails to save if invalid' do
      form = AdminUsers::RegistrationForm.new(params.except(:first_name))
      expect { form.save }.not_to change(AdminUser, :count)
      expect(form.errors.full_messages).to include 'First nameを入力してください'
    end
  end

  context 'if admin_user is persisted' do
    let(:admin_user) { create(:admin_user, first_name: 'old_name') }
    let(:params) { { first_name: 'updated_name' } }

    it 'saves if valid' do
      expect do
        form = AdminUsers::RegistrationForm.new(params, admin_user)
        form.save
      end.to change { admin_user.reload.first_name }.from('old_name').to('updated_name')
    end

    it 'fails to save if invalid' do
      form = nil
      expect do
        form = AdminUsers::RegistrationForm.new(params.merge(first_name: ''), admin_user)
        form.save
      end.not_to change { admin_user.reload.first_name }.from('old_name')
      expect(form.errors.full_messages).to include 'First Nameを入力してください'
    end
  end
end