Rails Model Patterns Skill

Rails Model Patterns

Patterns for building well-structured ActiveRecord models in Rails applications.

When This Skill Applies

Designing models with proper associations
Implementing validations and callbacks
Creating efficient scopes and queries
Writing safe database migrations
Optimizing database performance

Quick Reference

| Pattern | Use When | |---------|----------| | belongs_to | Child references parent | | has_many | Parent has multiple children | | has_one | Parent has single child | | has_many :through | Many-to-many via join model | | has_and_belongs_to_many | Simple many-to-many (no join model attributes) |

Detailed Documentation

associations.md - Association patterns and options
validations.md - Validation patterns
migrations.md - Safe migration practices

Model Structure Best Practice

class User < ApplicationRecord
  # 1. Constants
  ROLES = %w[admin member guest].freeze

  # 2. Associations
  belongs_to :organization
  has_many :posts, dependent: :destroy
  has_many :comments, through: :posts

  # 3. Validations
  validates :email, presence: true, uniqueness: { case_sensitive: false }
  validates :name, presence: true, length: { maximum: 100 }
  validates :role, inclusion: { in: ROLES }

  # 4. Scopes
  scope :active, -> { where(active: true) }
  scope :recent, -> { order(created_at: :desc) }
  scope :admins, -> { where(role: 'admin') }

  # 5. Callbacks (use sparingly)
  before_save :normalize_email

  # 6. Class methods
  def self.find_by_email(email)
    find_by(email: email.downcase.strip)
  end

  # 7. Instance methods
  def admin?
    role == 'admin'
  end

  private

  def normalize_email
    self.email = email.downcase.strip
  end
end

Key Principles

Validations

Use built-in validators when possible
Add database constraints for critical validations
Custom validators for complex business rules

Associations

Always specify :dependent option
Use :inverse_of for bidirectional associations
Consider counter caches for counts

Scopes

Prefer scopes over class methods for queries
Chain scopes for complex queries
Use merge to combine scopes from different models

Callbacks

Use sparingly - prefer service objects
Keep callbacks focused and simple
Avoid callbacks that trigger external services

Agent Skills: Rails Model Patterns

Skill Files