Methods

Attributes

[RW] abstract_class

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 behaviour:

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.

Instance Public methods

abstract_class?()

Returns whether this class is an abstract class or not.

📝 Source code 
# File activerecord/lib/active_record/inheritance.rb, line 163
      def abstract_class?
        defined?(@abstract_class) && @abstract_class == true
      end
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base_class()

Returns the class descending directly from ActiveRecord::Base, or an abstract class, if any, in the inheritance hierarchy.

If A extends ActiveRecord::Base, A.base_class will return A. If B descends from A through some arbitrarily deep hierarchy, B.base_class will return A.

If B < A and C < B and if A is an abstract_class then both B.base_class and C.base_class would return B as the answer since A is an abstract_class.

📝 Source code 
# File activerecord/lib/active_record/inheritance.rb, line 101
      def base_class
        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
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base_class?()

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

📝 Source code 
# File activerecord/lib/active_record/inheritance.rb, line 115
      def base_class?
        base_class == self
      end
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descends_from_active_record?()

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

📝 Source code 
# File activerecord/lib/active_record/inheritance.rb, line 78
      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
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inherited(subclass)

📝 Source code 
# File activerecord/lib/active_record/inheritance.rb, line 205
      def inherited(subclass)
        subclass.instance_variable_set(:@_type_candidates_cache, Concurrent::Map.new)
        super
      end
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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.

📝 Source code 
# File activerecord/lib/active_record/inheritance.rb, line 52
      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
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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.

📝 Source code 
# File activerecord/lib/active_record/inheritance.rb, line 197
      def polymorphic_class_for(name)
        if store_full_class_name
          ActiveSupport::Dependencies.constantize(name)
        else
          compute_type(name)
        end
      end
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polymorphic_name()

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

📝 Source code 
# File activerecord/lib/active_record/inheritance.rb, line 190
      def polymorphic_name
        store_full_class_name ? base_class.name : base_class.name.demodulize
      end
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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.

📝 Source code 
# File activerecord/lib/active_record/inheritance.rb, line 175
      def sti_class_for(type_name)
        if store_full_sti_class && store_full_class_name
          ActiveSupport::Dependencies.constantize(type_name)
        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
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sti_name()

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

📝 Source code 
# File activerecord/lib/active_record/inheritance.rb, line 168
      def sti_name
        store_full_sti_class && store_full_class_name ? name : name.demodulize
      end
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Instance Protected methods

compute_type(type_name)

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.

📝 Source code 
# File activerecord/lib/active_record/inheritance.rb, line 213
        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.
            ActiveSupport::Dependencies.constantize(type_name)
          else
            type_candidate = @_type_candidates_cache[type_name]
            if type_candidate && type_constant = ActiveSupport::Dependencies.safe_constantize(type_candidate)
              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 = ActiveSupport::Dependencies.safe_constantize(candidate)
              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
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