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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?
  @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.


  





  


  [ GitHub ]


  

  


# 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


  








  

    #finder_needs_type_condition?  ⇒ Boolean  (readonly)
  

  

    This method is for internal use only.
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 92



def finder_needs_type_condition? # :nodoc:
  # This is like this because benchmarking justifies the strange :false stuff
  :true == (@finder_needs_type_condition ||= descends_from_active_record? ? :false : :true)
end


  







Instance Method Details



  

    #compute_type(type_name)   (protected)
  



  

    

Returns the class type of the record using the current module as a prefix. So descendants of MyApp::Business::Account would appear as MyApp::Business::AccountSubclass.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 242



def compute_type(type_name)
  if type_name.start_with?("::")
    # If the type is prefixed with a scope operator then we assume that
    # the type_name is an absolute reference.
    type_name.constantize
  else
    type_candidate = @_type_candidates_cache[type_name]
    if type_candidate && type_constant = type_candidate.safe_constantize
      return type_constant
    end

    # Build a list of candidates to search for
    candidates = []
    name.scan(/::|$/) { candidates.unshift "#{$`}::#{type_name}" }
    candidates << type_name

    candidates.each do |candidate|
      constant = candidate.safe_constantize
      if candidate == constant.to_s
        @_type_candidates_cache[type_name] = candidate
        return constant
      end
    end

    raise NameError.new("uninitialized constant #{candidates.first}", candidates.first)
  end
end


  








  

    #discriminate_class_for_record(record)   (private)
  



  

    

Called by instantiate to decide which class to use for a new record instance. For single-table inheritance, we check the record for a type column and return the corresponding class.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 299



def discriminate_class_for_record(record)
  if using_single_table_inheritance?(record)
    find_sti_class(record[inheritance_column])
  else
    super
  end
end


  








  

    #dup  
  

  

    This method is for internal use only.
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 226



def dup # :nodoc:
  # `initialize_dup` / `initialize_copy` don't work when defined
  # in the `singleton_class`.
  other = super
  other.set_base_class
  other
end


  








  

    #find_sti_class(type_name)   (private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 311



def find_sti_class(type_name)
  type_name = base_class.type_for_attribute(inheritance_column).cast(type_name)
  subclass = sti_class_for(type_name)

  unless subclass == self || descendants.include?(subclass)
    raise SubclassNotFound, "Invalid single-table inheritance type: #{subclass.name} is not a subclass of #{name}"
  end

  subclass
end


  








  

    #inherited(subclass)   (private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 287



def inherited(subclass)
  super
  subclass.set_base_class
  subclass.instance_variable_set(:@_type_candidates_cache, Concurrent::Map.new)
  subclass.class_eval do
    @finder_needs_type_condition = nil
  end
end


  








  

    #initialize_clone(other)  
  

  

    This method is for internal use only.
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 234



def initialize_clone(other) # :nodoc:
  super
  set_base_class
end


  








  

    #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.


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 218



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 211



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.


  



  [ GitHub ]


  

  


# 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


  








  

    #set_base_class   (protected)
  

  

    This method is for internal use only.
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 270



def set_base_class # :nodoc:
  @base_class = if self == Base
    self
  else
    unless self < Base
      raise ActiveRecordError, "#{name} doesn't belong in a hierarchy descending from ActiveRecord"
    end

    if superclass == Base || superclass.abstract_class?
      self
    else
      superclass.base_class
    end
  end
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. " \
    "If you wish to disable single-table inheritance for #{name} set " \
    "#{name}.inheritance_column to nil"
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


  








  

    #subclass_from_attributes(attrs)   (private)
  



  

    

Detect the subclass from the inheritance column of attrs. If the inheritance column value is not self or a valid subclass, raises ::ActiveRecord::SubclassNotFound


  



  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 331



def subclass_from_attributes(attrs)
  attrs = attrs.to_h if attrs.respond_to?(:permitted?)
  if attrs.is_a?(Hash)
    subclass_name = attrs[inheritance_column] || attrs[inheritance_column.to_sym]

    if subclass_name.present?
      find_sti_class(subclass_name)
    end
  end
end


  








  

    #type_condition(table = arel_table)   (private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 322



def type_condition(table = arel_table)
  sti_column = table[inheritance_column]
  sti_names  = ([self] + descendants).map(&:sti_name)

  predicate_builder.build(sti_column, sti_names)
end


  








  

    #using_single_table_inheritance?(record)  ⇒ Boolean  (private)
  



  

    
  





  


  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/inheritance.rb', line 307



def using_single_table_inheritance?(record)
  record[inheritance_column].present? && _has_attribute?(inheritance_column)
end