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