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 lib/active_record/inheritance.rb, line 99 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 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.
# File lib/active_record/inheritance.rb, line 69 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 lib/active_record/inheritance.rb, line 36 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
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 17 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 subclass_from_attributes?(attrs) subclass = subclass_from_attributes(attrs) end if subclass subclass.new(*args, &block) else super end end
# File lib/active_record/inheritance.rb, line 103 def sti_name store_full_sti_class ? name : name.demodulize end
# File lib/active_record/inheritance.rb, line 51 def symbolized_base_class ActiveSupport::Deprecation.warn("ActiveRecord::Base.symbolized_base_class is deprecated and will be removed without replacement.") @symbolized_base_class ||= base_class.to_s.to_sym end
# File lib/active_record/inheritance.rb, line 56 def symbolized_sti_name ActiveSupport::Deprecation.warn("ActiveRecord::Base.symbolized_sti_name is deprecated and will be removed without replacement.") @symbolized_sti_name ||= sti_name.present? ? sti_name.to_sym : symbolized_base_class 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 111 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 # We don't want to swallow NoMethodError < NameError errors rescue NoMethodError raise rescue NameError 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 142 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 154 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
# File lib/active_record/inheritance.rb, line 183 def subclass_from_attributes(attrs) subclass_name = attrs.with_indifferent_access[inheritance_column] if subclass_name.present? && subclass_name != self.name subclass = subclass_name.safe_constantize unless descendants.include?(subclass) raise ActiveRecord::SubclassNotFound.new("Invalid single-table inheritance type: #{subclass_name} is not a subclass of #{name}") end subclass end 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
# File lib/active_record/inheritance.rb, line 179 def subclass_from_attributes?(attrs) columns_hash.include?(inheritance_column) && attrs.is_a?(Hash) end
# File lib/active_record/inheritance.rb, line 168 def type_condition(table = arel_table) sti_column = table[inheritance_column] sti_names = ([self] + descendants).map { |model| model.sti_name } sti_column.in(sti_names) end
# File lib/active_record/inheritance.rb, line 150 def using_single_table_inheritance?(record) record[inheritance_column].present? && columns_hash.include?(inheritance_column) end