module ActiveRecord module Inheritance extend ActiveSupport::Concern included do # Determine whether to store the full constant name including namespace when using STI class_attribute :store_full_sti_class, instance_writer: false self.store_full_sti_class = true end module ClassMethods # 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 def new(*args, &block) if (attrs = args.first).is_a?(Hash) if subclass = subclass_from_attrs(attrs) return subclass.new(*args, &block) end end # Delegate to the original .new super end # True if this isn't a concrete subclass needing a STI type condition. 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 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 def symbolized_base_class @symbolized_base_class ||= base_class.to_s.to_sym end def symbolized_sti_name @symbolized_sti_name ||= sti_name.present? ? sti_name.to_sym : symbolized_base_class end # Returns the class descending directly from ActiveRecord::Base, or # an abstract class, if any, in the inheritance hierarchy. # # If A extends AR::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. 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 # Set this to true if this is an abstract class (see abstract_class?). # If you are using inheritance with ActiveRecord and don't want child classes # to utilize the implied STI table name of the parent class, this will need to be true. # For example, given the following: # # class SuperClass < ActiveRecord::Base # self.abstract_class = true # end # class Child < SuperClass # self.table_name = 'the_table_i_really_want' # end # # # self.abstract_class = true is required to make Child<.find,.create, or any Arel method> use the_table_i_really_want instead of a table called super_classes # attr_accessor :abstract_class # Returns whether this class is an abstract class or not. def abstract_class? defined?(@abstract_class) && @abstract_class == true end def sti_name store_full_sti_class ? name : name.demodulize end 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. def compute_type(type_name) if type_name.match(/^::/) # 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 # Build a list of candidates to search for candidates = [] name.scan(/::|$/) { candidates.unshift "#{$`}::#{type_name}" } candidates << type_name candidates.each do |candidate| begin constant = ActiveSupport::Dependencies.constantize(candidate) return constant if candidate == constant.to_s rescue NameError => e # We don't want to swallow NoMethodError < NameError errors raise e unless e.instance_of?(NameError) end end raise NameError, "uninitialized constant #{candidates.first}" end end 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. def discriminate_class_for_record(record) if using_single_table_inheritance?(record) find_sti_class(record[inheritance_column]) else super end end def using_single_table_inheritance?(record) record[inheritance_column].present? && columns_hash.include?(inheritance_column) end def find_sti_class(type_name) 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 def type_condition(table = arel_table) sti_column = table[inheritance_column.to_sym] sti_names = ([self] + descendants).map { |model| model.sti_name } sti_column.in(sti_names) 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 # If this is a StrongParameters hash, and access to inheritance_column is not permitted, # this will ignore the inheritance column and return nil def subclass_from_attrs(attrs) subclass_name = attrs.with_indifferent_access[inheritance_column] return nil if subclass_name.blank? || subclass_name == self.name unless subclass = subclasses.detect { |sub| sub.name == subclass_name } raise ActiveRecord::SubclassNotFound.new("Invalid single-table inheritance type: #{subclass_name} is not a subclass of #{name}") end subclass end end private # Sets the attribute used for single table inheritance to this class name if this is not the # ActiveRecord::Base descendant. # Considering the hierarchy Reply < Message < ActiveRecord::Base, this makes it possible to # do Reply.new without having to set Reply[Reply.inheritance_column] = "Reply" yourself. # No such attribute would be set for objects of the Message class in that example. def ensure_proper_type klass = self.class if klass.finder_needs_type_condition? write_attribute(klass.inheritance_column, klass.sti_name) end end end end