module ActiveRecord::Inheritance::ClassMethods
Attributes
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.
Public Instance Methods
Returns whether this class is an abstract class or not.
# File lib/active_record/inheritance.rb, line 160 def abstract_class? defined?(@abstract_class) && @abstract_class == true end
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.
# File lib/active_record/inheritance.rb, line 98 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
Returns whether the class is a base class. See base_class for more information.
# File lib/active_record/inheritance.rb, line 112 def base_class? base_class == self end
Returns true
if this does not need STI type condition. Returns
false
if STI type condition needs to be applied.
# File lib/active_record/inheritance.rb, line 75 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
# File lib/active_record/inheritance.rb, line 172 def inherited(subclass) subclass.instance_variable_set(:@_type_candidates_cache, Concurrent::Map.new) super end
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.
# File lib/active_record/inheritance.rb, line 49 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
# File lib/active_record/inheritance.rb, line 168 def polymorphic_name base_class.name end
# File lib/active_record/inheritance.rb, line 164 def sti_name store_full_sti_class ? name : name.demodulize end
Protected Instance Methods
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.
# File lib/active_record/inheritance.rb, line 180 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
Private Instance Methods
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.
# File lib/active_record/inheritance.rb, line 212 def discriminate_class_for_record(record) if using_single_table_inheritance?(record) find_sti_class(record[inheritance_column]) else super end end
# File lib/active_record/inheritance.rb, line 224 def find_sti_class(type_name) type_name = base_class.type_for_attribute(inheritance_column).cast(type_name) subclass = begin if store_full_sti_class 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 unless subclass == self || descendants.include?(subclass) raise SubclassNotFound, "Invalid single-table inheritance type: #{subclass.name} is not a subclass of #{name}" end subclass end
Detect the subclass from the inheritance column of attrs. If the inheritance column value is not self or a valid subclass, raises ActiveRecord::SubclassNotFound
# File lib/active_record/inheritance.rb, line 254 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
# File lib/active_record/inheritance.rb, line 245 def type_condition(table = arel_table) sti_column = arel_attribute(inheritance_column, table) sti_names = ([self] + descendants).map(&:sti_name) predicate_builder.build(sti_column, sti_names) end
# File lib/active_record/inheritance.rb, line 220 def using_single_table_inheritance?(record) record[inheritance_column].present? && has_attribute?(inheritance_column) end