Added ActiveRecord::Recursion to guard against recursive calls to #save

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@1411 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

1 files changed, 60 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/recursion.rb b/activerecord/lib/active_record/recursion.rb
new file mode 100644
index 0000000000..36589238e7
--- /dev/null
+++ b/activerecord/lib/active_record/recursion.rb
@@ -0,0 +1,60 @@
+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