Rails Model Generator (TDD Approach)

Overview

This skill creates models the TDD way:

• Define requirements (attributes, validations, associations)

• Write model spec with expected behavior (RED)

• Create factory for test data

• Generate migration

• Implement model to pass specs (GREEN)

• Refactor if needed

Workflow Checklist

Model Creation Progress:

• Step 1: Define requirements (attributes, validations, associations)
• Step 2: Create model spec (RED)
• Step 3: Create factory
• Step 4: Run spec (should fail - no model/table)
• Step 5: Generate migration
• Step 6: Run migration
• Step 7: Create model file (empty)
• Step 8: Run spec (should fail - no validations)
• Step 9: Add validations and associations
• Step 10: Run spec (GREEN)

Step 1: Requirements Template

Before writing code, define the model:

Model: [ModelName]

Table: [table_name]

Attributes

Associations

• belongs_to :organization
• has_many :posts, dependent: :destroy
• has_one :profile, dependent: :destroy

Validations

• name: presence, uniqueness, length(max: 100)
• email: presence, uniqueness, format(email)
• status: inclusion in enum values

Scopes

• active: status = active
• recent: ordered by created_at desc
• by_organization(org): where organization_id = org.id

Instance Methods

• full_name: combines first_name and last_name
• active?: checks if status is active

Callbacks

• before_save :normalize_email
• after_create :send_welcome_email

Step 2: Create Model Spec

Location: spec/models/[model_name]_spec.rb

frozen_string_literal: true

require 'rails_helper'

RSpec.describe ModelName, type: :model do subject { build(:model_name) }

=== Associations ===

describe 'associations' do it { is_expected.to belong_to(:organization) } it { is_expected.to have_many(:posts).dependent(:destroy) } end

=== Validations ===

describe 'validations' do it { is_expected.to validate_presence_of(:name) } it { is_expected.to validate_uniqueness_of(:email).case_insensitive } it { is_expected.to validate_length_of(:name).is_at_most(100) } end

=== Scopes ===

describe '.active' do let!(:active_record) { create(:model_name, status: :active) } let!(:inactive_record) { create(:model_name, status: :inactive) }

it 'returns only active records' do
  expect(described_class.active).to include(active_record)
  expect(described_class.active).not_to include(inactive_record)
end

end

=== Instance Methods ===

describe '#full_name' do subject { build(:model_name, first_name: 'John', last_name: 'Doe') }

it 'returns combined name' do
  expect(subject.full_name).to eq('John Doe')
end

end end

Step 3: Create Factory

Location: spec/factories/[model_name_plural].rb

frozen_string_literal: true

FactoryBot.define do factory :model_name do sequence(:name) { |n| "Name #{n}" } sequence(:email) { |n| "user#{n}@example.com" } status { :pending } association :organization

trait :active do
  status { :active }
end

trait :with_posts do
  after(:create) do |record|
    create_list(:post, 3, model_name: record)
  end
end

end end

Step 4: Run Spec (Verify RED)

bundle exec rspec spec/models/model_name_spec.rb

Expected: Failure because model/table doesn't exist.

Step 5: Generate Migration

bin/rails generate migration CreateModelNames
name:string
email:string:uniq
status:integer
organization:references

Review the generated migration and add:

• Null constraints: null: false

• Defaults: default: 0

• Indexes: add_index :table, :column

db/migrate/YYYYMMDDHHMMSS_create_model_names.rb

class CreateModelNames < ActiveRecord::Migration[8.0] def change create_table :model_names do |t| t.string :name, null: false t.string :email, null: false t.integer :status, null: false, default: 0 t.references :organization, null: false, foreign_key: true

  t.timestamps
end

add_index :model_names, :email, unique: true
add_index :model_names, :status

end end

Step 6: Run Migration

bin/rails db:migrate

Verify with:

bin/rails db:migrate:status

Step 7: Create Model File

Location: app/models/[model_name].rb

frozen_string_literal: true

class ModelName < ApplicationRecord end

Step 8: Run Spec (Still RED)

bundle exec rspec spec/models/model_name_spec.rb

Expected: Failures for missing validations/associations.

Step 9: Add Validations & Associations

frozen_string_literal: true

class ModelName < ApplicationRecord

=== Associations ===

belongs_to :organization has_many :posts, dependent: :destroy

=== Enums ===

enum :status, { pending: 0, active: 1, suspended: 2 }

=== Validations ===

validates :name, presence: true, uniqueness: true, length: { maximum: 100 } validates :email, presence: true, uniqueness: { case_sensitive: false }, format: { with: URI::MailTo::EMAIL_REGEXP }

=== Scopes ===

scope :active, -> { where(status: :active) } scope :recent, -> { order(created_at: :desc) }

=== Instance Methods ===

def full_name "#{first_name} #{last_name}".strip end end

Step 10: Run Spec (GREEN)

bundle exec rspec spec/models/model_name_spec.rb

All specs should pass.

References

• See reference/validations.md for validation patterns

Common Patterns

Enum with Validation

enum :status, { draft: 0, published: 1, archived: 2 } validates :status, inclusion: { in: statuses.keys }

Polymorphic Association

belongs_to :commentable, polymorphic: true

Counter Cache

belongs_to :organization, counter_cache: true

Add: organization.posts_count column

Soft Delete

scope :active, -> { where(deleted_at: nil) } scope :deleted, -> { where.not(deleted_at: nil) }

def soft_delete update(deleted_at: Time.current) end