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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
class_name.foreign_key
elsif options[:as]
"#{options[:as]}_id"
else
active_record.name.foreign_key
end
end
end
end
end
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