module ActiveRecord module Reflection # :nodoc: def self.included(base) base.extend(ClassMethods) end # Reflection allows you to interrogate Active Record classes and objects about their associations and aggregations. # This information can, for example, be used in a form builder that took an Active Record object and created input # fields for all of the attributes depending on their type and displayed the associations to other objects. # # You can find the interface for the AggregateReflection and AssociationReflection classes in the abstract MacroReflection class. module ClassMethods def create_reflection(macro, name, options, active_record) case macro when :has_many, :belongs_to, :has_one, :has_and_belongs_to_many reflection = AssociationReflection.new(macro, name, options, active_record) when :composed_of reflection = AggregateReflection.new(macro, name, options, active_record) end write_inheritable_hash :reflections, name => reflection reflection end # Returns a hash containing all AssociationReflection objects for the current class # Example: # # Invoice.reflections # Account.reflections # def reflections read_inheritable_attribute(:reflections) || write_inheritable_attribute(:reflections, {}) end # Returns an array of AggregateReflection objects for all the aggregations in the class. def reflect_on_all_aggregations reflections.values.select { |reflection| reflection.is_a?(AggregateReflection) } end # Returns the AggregateReflection object for the named +aggregation+ (use the symbol). Example: # # Account.reflect_on_aggregation(:balance) # returns the balance AggregateReflection # def reflect_on_aggregation(aggregation) reflections[aggregation].is_a?(AggregateReflection) ? reflections[aggregation] : nil end # Returns an array of AssociationReflection objects for all the aggregations in the class. If you only want to reflect on a # certain association type, pass in the symbol (:has_many, :has_one, :belongs_to) for that as the first parameter. # Example: # # Account.reflect_on_all_associations # returns an array of all associations # Account.reflect_on_all_associations(:has_many) # returns an array of all has_many associations # def reflect_on_all_associations(macro = nil) association_reflections = reflections.values.select { |reflection| reflection.is_a?(AssociationReflection) } macro ? association_reflections.select { |reflection| reflection.macro == macro } : association_reflections end # Returns the AssociationReflection object for the named +aggregation+ (use the symbol). Example: # # Account.reflect_on_association(:owner) # returns the owner AssociationReflection # Invoice.reflect_on_association(:line_items).macro # returns :has_many # def reflect_on_association(association) reflections[association].is_a?(AssociationReflection) ? reflections[association] : nil end end # Abstract base class for AggregateReflection and AssociationReflection that describes the interface available for both of # those classes. Objects of AggregateReflection and AssociationReflection are returned by the Reflection::ClassMethods. class MacroReflection attr_reader :active_record def initialize(macro, name, options, active_record) @macro, @name, @options, @active_record = macro, name, options, active_record end # Returns the name of the macro, so it would return :balance for "composed_of :balance, :class_name => 'Money'" or # :clients for "has_many :clients". def name @name end # Returns the name of the macro, so it would return :composed_of for # "composed_of :balance, :class_name => 'Money'" or :has_many for "has_many :clients". def macro @macro end # Returns the hash of options used for the macro, so it would return { :class_name => "Money" } for # "composed_of :balance, :class_name => 'Money'" or {} for "has_many :clients". def options @options end # Returns the class for the macro, so "composed_of :balance, :class_name => 'Money'" returns the Money class and # "has_many :clients" returns the Client class. def klass @klass ||= class_name.constantize end def class_name @class_name ||= options[:class_name] || derive_class_name end def ==(other_aggregation) name == other_aggregation.name && other_aggregation.options && active_record == other_aggregation.active_record end private def derive_class_name name.to_s.camelize end end # Holds all the meta-data about an aggregation as it was specified in the Active Record class. class AggregateReflection < MacroReflection #:nodoc: end # Holds all the meta-data about an association as it was specified in the Active Record class. class AssociationReflection < MacroReflection #:nodoc: def klass @klass ||= active_record.send(:compute_type, class_name) end def table_name @table_name ||= klass.table_name end def primary_key_name @primary_key_name ||= options[:foreign_key] || derive_primary_key_name end def association_foreign_key @association_foreign_key ||= @options[:association_foreign_key] || class_name.foreign_key end def counter_cache_column if options[:counter_cache] == true "#{active_record.name.underscore.pluralize}_count" elsif options[:counter_cache] options[:counter_cache] end end def through_reflection @through_reflection ||= options[:through] ? active_record.reflect_on_association(options[:through]) : false end # Gets an array of possible :through source reflection names # # [singularized, pluralized] # def source_reflection_names @source_reflection_names ||= (options[:source] ? [options[:source]] : [name.to_s.singularize, name]).collect { |n| n.to_sym } end # Gets the source of the through reflection. It checks both a singularized and pluralized form for :belongs_to or :has_many. # (The :tags association on Tagging below) # # class Post # has_many :tags, :through => :taggings # end # def source_reflection return nil unless through_reflection @source_reflection ||= source_reflection_names.collect { |name| through_reflection.klass.reflect_on_association(name) }.compact.first end def check_validity! if options[:through] if through_reflection.nil? raise HasManyThroughAssociationNotFoundError.new(active_record.name, self) end if source_reflection.nil? raise HasManyThroughSourceAssociationNotFoundError.new(self) end if options[:source_type] && source_reflection.options[:polymorphic].nil? raise HasManyThroughAssociationPointlessSourceTypeError.new(active_record.name, self, source_reflection) end if source_reflection.options[:polymorphic] && options[:source_type].nil? raise HasManyThroughAssociationPolymorphicError.new(active_record.name, self, source_reflection) end unless [:belongs_to, :has_many].include?(source_reflection.macro) && source_reflection.options[:through].nil? raise HasManyThroughSourceAssociationMacroError.new(self) end end end private def derive_class_name # get the class_name of the belongs_to association of the through reflection if through_reflection options[:source_type] || source_reflection.class_name else class_name = name.to_s.camelize class_name = class_name.singularize if [ :has_many, :has_and_belongs_to_many ].include?(macro) class_name end end def derive_primary_key_name if macro == :belongs_to "#{name}_id" elsif options[:as] "#{options[:as]}_id" else active_record.name.foreign_key end end end end end