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module ActiveRecord
# Wraps a guard around #save to make sure that recursive calls don't actually
# invoke save multiple times. Recursive calls to save can occur quite
# easily, and unintentionally. Consider the following case:
#
# class Project < ActiveRecord::Base
# has_and_belongs_to_many :people
# after_create :grant_access_to_admins
#
# def grant_access_to_admins
# Person.admins.each do |admin|
# admin.projects.push_with_attributes(self, "access_level" => 42)
# end
# end
# end
#
# class Person < ActiveRecord::Base
# has_and_belongs_to_many :projects
# ...
# end
#
# teddy = Person.find_by_name("teddy")
# project = Project.new :name => "sumo wrestling"
# project.people << teddy
# project.save!
#
# The #push_with_attributes causes +self+ (the project) to be saved again,
# even though we're already in the midst of doing a save. This results in
# "teddy" _not_ being added to the project's people list, because the
# recursive call resets the new-record status and thus ignores any
# non-new records in the collection.
#
# Thus, the need for a recursive guard on save.
module Recursion
def self.append_features(base) # :nodoc:
super
base.class_eval do
alias_method :save_without_recursive_guard, :save
alias_method :save, :save_with_recursive_guard
end
end
# Wrap the save call with a sentinel that prevents saves from occuring if
# a save is already in progress.
def save_with_recursive_guard(*args)
critical = Thread.critical
Thread.critical = true
old_save_state = @currently_saving_record
return true if @currently_saving_record
@currently_saving_record = true
Thread.critical = critical
save_without_recursive_guard(*args)
ensure
Thread.critical = critical
@currently_saving_record = old_save_state
end
end
end
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