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Module: ActiveRecord::Inheritance::ClassMethods

Relationships & Source Files
Defined in: activerecord/lib/active_record/inheritance.rb

Instance Attribute Summary

Instance Method Summary

Instance Attribute Details

#abstract_class (rw)

Set this to true if this is an abstract class (see #abstract_class?). If you are using inheritance with Active Record and don’t want a class to be considered as part of the STI hierarchy, you must set this to true. ApplicationRecord, for example, is generated as an abstract class.

Consider the following default behavior:

Shape = Class.new(ActiveRecord::Base)
Polygon = Class.new(Shape)
Square = Class.new(Polygon)

Shape.table_name   # => "shapes"
Polygon.table_name # => "shapes"
Square.table_name  # => "shapes"
Shape.create!      # => #<Shape id: 1, type: nil>
Polygon.create!    # => #<Polygon id: 2, type: "Polygon">
Square.create!     # => #<Square id: 3, type: "Square">

However, when using abstract_class, Shape is omitted from the hierarchy:

class Shape < ActiveRecord::Base
  self.abstract_class = true
end
Polygon = Class.new(Shape)
Square = Class.new(Polygon)

Shape.table_name   # => nil
Polygon.table_name # => "polygons"
Square.table_name  # => "polygons"
Shape.create!      # => NotImplementedError: Shape is an abstract class and cannot be instantiated.
Polygon.create!    # => #<Polygon id: 1, type: nil>
Square.create!     # => #<Square id: 2, type: "Square">

Note that in the above example, to disallow the creation of a plain Polygon, you should use validates :type, presence: true, instead of setting it as an abstract class. This way, Polygon will stay in the hierarchy, and Active Record will continue to correctly derive the table name.

[ GitHub ] 

  


# File 'activerecord/lib/active_record/inheritance.rb', line 164



attr_accessor :abstract_class


  








  

    #abstract_class?  ⇒ Boolean  (rw)
  



  

    

Returns whether this class is an abstract class or not.


  





  


  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 167



def abstract_class?
  defined?(@abstract_class) && @abstract_class == true
end


  








  

    #base_class   (readonly)
  



  

    

Returns the first class in the inheritance hierarchy that descends from either an abstract class or from ::ActiveRecord::Base.



Consider the following behaviour:



class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true
end
class Shape < ApplicationRecord
  self.abstract_class = true
end
Polygon = Class.new(Shape)
Square = Class.new(Polygon)

ApplicationRecord.base_class # => ApplicationRecord
Shape.base_class # => Shape
Polygon.base_class # => Polygon
Square.base_class # => Polygon


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 115



attr_reader :base_class


  








  

    #base_class?  ⇒ Boolean  (readonly)
  



  

    

Returns whether the class is a base class. See #base_class for more information.


  





  


  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 119



def base_class?
  base_class == self
end


  








  

    #descends_from_active_record?  ⇒ Boolean  (readonly)
  



  

    

Returns true if this does not need STI type condition. Returns false if STI type condition needs to be applied.


  





  


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# File 'activerecord/lib/active_record/inheritance.rb', line 82



def descends_from_active_record?
  if self == Base
    false
  elsif superclass.abstract_class?
    superclass.descends_from_active_record?
  else
    superclass == Base || !columns_hash.include?(inheritance_column)
  end
end


  







Instance Method Details



  

    #new(attributes = nil, &block)  
  



  

    

Determines if one of the attributes passed in is the inheritance column, and if the inheritance column is attr accessible, it initializes an instance of the given subclass instead of the base class.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 56



def new(attributes = nil, &block)
  if abstract_class? || self == Base
    raise NotImplementedError, "#{self} is an abstract class and cannot be instantiated."
  end

  if _has_attribute?(inheritance_column)
    subclass = subclass_from_attributes(attributes)

    if subclass.nil? && scope_attributes = current_scope&.scope_for_create
      subclass = subclass_from_attributes(scope_attributes)
    end

    if subclass.nil? && base_class?
      subclass = subclass_from_attributes(column_defaults)
    end
  end

  if subclass && subclass != self
    subclass.new(attributes, &block)
  else
    super
  end
end


  








  

    #polymorphic_class_for(name)  
  



  

    

Returns the class for the provided name.



It is used to find the class correspondent to the value stored in the polymorphic type column.


  



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# File 'activerecord/lib/active_record/inheritance.rb', line 216



def polymorphic_class_for(name)
  if store_full_class_name
    name.constantize
  else
    compute_type(name)
  end
end


  








  

    #polymorphic_name  
  



  

    

Returns the value to be stored in the polymorphic type column for Polymorphic Associations.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 209



def polymorphic_name
  store_full_class_name ? base_class.name : base_class.name.demodulize
end


  








  

    #primary_abstract_class  
  



  

    

Sets the application record class for Active Record



This is useful if your application uses a different class than ApplicationRecord for your primary abstract class. This class will share a database connection with Active Record. It is the class that connects to your primary database.


  



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# File 'activerecord/lib/active_record/inheritance.rb', line 177



def primary_abstract_class
  if ActiveRecord.application_record_class && ActiveRecord.application_record_class.name != name
    raise ArgumentError, "The `primary_abstract_class` is already set to #{ActiveRecord.application_record_class.inspect}. There can only be one `primary_abstract_class` in an application."
  end

  self.abstract_class = true
  ActiveRecord.application_record_class = self
end


  








  

    #sti_class_for(type_name)  
  



  

    

Returns the class for the provided type_name.



It is used to find the class correspondent to the value stored in the inheritance column.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 194



def sti_class_for(type_name)
  if store_full_sti_class && store_full_class_name
    type_name.constantize
  else
    compute_type(type_name)
  end
rescue NameError
  raise SubclassNotFound,
    "The single-table inheritance mechanism failed to locate the subclass: '#{type_name}'. " \
    "This error is raised because the column '#{inheritance_column}' is reserved for storing the class in case of inheritance. " \
    "Please rename this column if you didn't intend it to be used for storing the inheritance class " \
    "or overwrite #{name}.inheritance_column to use another column for that information."
end


  








  

    #sti_name  
  



  

    

Returns the value to be stored in the inheritance column for STI.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 187



def sti_name
  store_full_sti_class && store_full_class_name ? name : name.demodulize
end