Rails Relationships

RubyOnRailsRelationshipNotes.rb

#------------------------------------------------------------------------------------------
#                               One to One Relationship
#------------------------------------------------------------------------------------------
class Subject < ActiveRecord::Base
  has_one :page
end

class Page < ActiveRecord::Base
  #Class with belongs_to should have the foreign key 
  #belongs_to :subject, {:foreign_key => "subject_id"}
  belongs_to :subject   #foreign key defaults to class_id so it does not need to be specified
end

#------------------------------------------------------------------------------------------
#                               One to Many
#------------------------------------------------------------------------------------------
class Subject < ActiveRecord::Base
  has_many :pages
end

class Page < ActiveRecord::Base
  belongs_to :subject   
  has_many :sections
end

class Section < ActiveRecord::Base
  belongs_to :page  
end

#------------------------------------------------------------------------------------------
#                               Many to Many - Simple
#------------------------------------------------------------------------------------------

#Need to create a join table
#NB - No primary key column (:id => false)
#Two foreign keys, index both keys together
#By default the table should be named first_table + _ + second_table in alphabetical order

class CreateAdminUsersPagesJoin < ActiveRecord::Migration
def change
    create_table :admin_users_pages, :id => false do |t|
	t.integer  :admin_user_id
        t.integer  :page_id
        t.timestamps
    end  
    add_index :admin_users_pages, [:admin_user_id, :page_id]
  end
end

#--------------------------------------------------

class AdminUser < ActiveRecord::Base
  has_and_belongs_to_many :pages
end

class Page < ActiveRecord::Base
  belongs_to :subject   
  has_many :sections
  has_and_belongs_to_many :admin_users

  #This can also be done as below, editors may make more sense than admin_users
  #has_and_belongs_to_many :editors, :class_name => "AdminUser"
end


#------------------------------------------------------------------------------------------
#                               Many to Many - Rich
#------------------------------------------------------------------------------------------

#Many to Many Rich requires a model
rails generate model SectionEdit

#NB - Needs to have a primary key :id
class CreateSectionEdits < ActiveRecord::Migration
def change
    create_table :sections_edits do |t|
	t.integer  :admin_user_id
        t.integer  :section_id
        
        t.string   :summary
    end  
    add_index :sections_edits, [:admin_user_id, :section_id]
  end
end

#--------------------------------------------------

class AdminUser < ActiveRecord::Base
  has_and_belongs_to_many :pages
  has_many :section_edits
end

class Section < ActiveRecord::Base
  belongs_to :page   
  has_many :section_edits
end

class SectionEdit < ActiveRecord::Base
  belongs_to_many :editors, :class_name => "AdminUser", :foreign_key => "admin_user_id"
  # same effect as - belongs_to :admin_user  
  belongs_to :section 
end

#--------------------------------------------------
# has_many :through - This simplifies the navigation

class AdminUser < ActiveRecord::Base
  has_and_belongs_to_many :pages
  has_many :section_edits
  has_many :sections, :through => :section_edits
end

class Section < ActiveRecord::Base
  belongs_to :page   
  has_many: section_edits
  has_many :editors, :through => :section_edits, :class_name => "AdminUser"
  #same as - has_many :admin_users, :through => :section_edits
end

class SectionEdit < ActiveRecord::Base
  belongs_to_many :editors, :class_name => "AdminUser", :foreign_key => "admin_user_id"
  # same effect as - belongs_to :admin_user  
  belongs_to :section 
end