module ActiveRecord::Inheritance::ClassMethods
Attributes
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
Public Instance Methods
Returns whether this class is an abstract class or not.
# File activerecord/lib/active_record/inheritance.rb, line 126 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 activerecord/lib/active_record/inheritance.rb, line 96 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 true
if this does not need STI type condition. Returns false
if STI type condition needs to be applied.
# File activerecord/lib/active_record/inheritance.rb, line 73 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 activerecord/lib/active_record/inheritance.rb, line 134 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 activerecord/lib/active_record/inheritance.rb, line 50 def new(*args, &block) if abstract_class? || self == Base raise NotImplementedError, "#{self} is an abstract class and cannot be instantiated." end attrs = args.first if has_attribute?(inheritance_column) subclass = subclass_from_attributes(attrs) if subclass.nil? && base_class == self subclass = subclass_from_attributes(column_defaults) end end if subclass && subclass != self subclass.new(*args, &block) else super end end
# File activerecord/lib/active_record/inheritance.rb, line 130 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 activerecord/lib/active_record/inheritance.rb, line 143 def compute_type(type_name) if type_name.start_with?("::".freeze) # 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 activerecord/lib/active_record/inheritance.rb, line 176 def discriminate_class_for_record(record) if using_single_table_inheritance?(record) find_sti_class(record[inheritance_column]) else super end end
# File activerecord/lib/active_record/inheritance.rb, line 188 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 activerecord/lib/active_record/inheritance.rb, line 218 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 activerecord/lib/active_record/inheritance.rb, line 209 def type_condition(table = arel_table) sti_column = arel_attribute(inheritance_column, table) sti_names = ([self] + descendants).map(&:sti_name) sti_column.in(sti_names) end
# File activerecord/lib/active_record/inheritance.rb, line 184 def using_single_table_inheritance?(record) record[inheritance_column].present? && has_attribute?(inheritance_column) end