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Module: ActiveRecord::Inheritance

Relationships & Source Files
Namespace Children
Modules:
Extension / Inclusion / Inheritance Descendants
Included In:
Base, ActiveRecord::InternalMetadata, ActiveRecord::SchemaMigration
Super Chains via Extension / Inclusion / Inheritance
Class Chain:
Defined in: activerecord/lib/active_record/inheritance.rb

Overview

Single table inheritance

Active Record allows inheritance by storing the name of the class in a column that by default is named “type” (can be changed by overwriting Base.inheritance_column). This means that an inheritance looking like this:

class Company < ActiveRecord::Base; end
class Firm < Company; end
class Client < Company; end
class PriorityClient < Client; end

When you do Firm.create(name: "37signals"), this record will be saved in the companies table with type = “Firm”. You can then fetch this row again using Company.where(name: '37signals').first and it will return a Firm object.

Be aware that because the type column is an attribute on the record every new subclass will instantly be marked as dirty and the type column will be included in the list of changed attributes on the record. This is different from non Single Table Inheritance(STI) classes:

Company.new.changed? # => false
Firm.new.changed?    # => true
Firm.new.changes     # => {"type"=>["","Firm"]}

If you don’t have a type column defined in your table, single-table inheritance won’t be triggered. In that case, it’ll work just like normal subclasses with no special magic for differentiating between them or reloading the right type with find.

Note, all the attributes for all the cases are kept in the same table. Read more: www.martinfowler.com/eaaCatalog/singleTableInheritance.html

Class Method Summary

Instance Method Summary

DSL Calls

included

[ GitHub ]


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# File 'activerecord/lib/active_record/inheritance.rb', line 40

included do
  # Determines whether to store the full constant name including namespace when using STI.
  # This is true, by default.
  class_attribute :store_full_sti_class, instance_writer: false, default: true
end

Instance Method Details

#initialize_dup(other)

[ GitHub ]

  
# File 'activerecord/lib/active_record/inheritance.rb', line 259

def initialize_dup(other)
  super
  ensure_proper_type
end