#394 STI and Polymorphic Associations pro

Nov 25, 2012 | 14 minutes | Active Record, Refactoring

Single Table Inheritance (STI) can help organize branching logic into separate classes, but a polymorphic association may be a better fit if there are unique database columns.

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Single Table Inheritance Solution

          terminal
        
rails g migration add_type_to_users type
rails g migration remove_guest_from_users guest:boolean
rake db:migrate

          models/user.rb
        
class User < ActiveRecord::Base
  has_many :tasks, dependent: :destroy
end

          models/guest.rb
        
class Guest < User
  def guest?
    true
  end
  
  def move_to(user)
    tasks.update_all(user_id: user.id)
  end
  
  def name
    "Guest"
  end

  def task_limit
    10
  end
  
  def can_share_task?(task)
    false
  end
  
  def send_password_reset
  end
end

          models/member.rb
        
class Member < User
  attr_accessible :username, :email, :password, :password_confirmation

  validates_presence_of :username, :email
  validates_uniqueness_of :username, allow_blank: true

  has_secure_password
  
  def guest?
    false
  end
  
  def name
    username
  end

  def task_limit
    1000
  end
  
  def can_share_task?(task)
    task.user_id == id
  end
  
  def send_password_reset
    UserMailer.password_reset(self).deliver
  end
end

Polymorphic Association Solution

          terminal
        
rails g migration remove_member_from_users username email password_digest type
rails g model MemberProfile username email password_digest
rails g model GuestProfile
rails g migration add_profile_to_users profile_id:integer profile_type

          models/user.rb
        
class User < ActiveRecord::Base
  has_many :tasks, dependent: :destroy
  belongs_to :profile, polymorphic: true

  delegate :guest?, :name, :can_share_task?, :send_password_reset, :become_member,
    to: :profile
end

          models/guest_profile.rb
        
class GuestProfile < ActiveRecord::Base
  has_one :user, as: :profile, dependent: :destroy

  def guest?
    true
  end

  def become_member(member_profile)
    user.profile = member_profile
    user.save!
  end

  def name
    "Guest"
  end

  def task_limit
    10
  end

  def can_share_task?(task)
    false
  end

  def send_password_reset
  end
end

          models/member_profile.rb
        
class MemberProfile < ActiveRecord::Base
  has_one :user, as: :profile, dependent: :destroy

  attr_accessible :username, :email, :password, :password_confirmation

  validates_presence_of :username, :email
  validates_uniqueness_of :username, allow_blank: true

  has_secure_password
  
  def guest?
    false
  end
  
  def name
    username
  end

  def task_limit
    1000
  end
  
  def can_share_task?(task)
    task.user_id == user.id
  end
  
  def send_password_reset
    UserMailer.password_reset(self).deliver
  end
end