Destroy associated has_and_belongs_to_many records after all before_destroy...

Destroy associated has_and_belongs_to_many records after all before_destroy callbacks but before destroy.  This allows you to act on the habtm association as you please while preserving referential integrity.  Closes #2065.

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@2940 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/CHANGELOG

 *SVN*
 
+* Destroy associated has_and_belongs_to_many records after all before_destroy callbacks but before destroy.  This allows you to act on the habtm association as you please while preserving referential integrity.  #2065 [larrywilliams1@gmail.com, sam.kirchmeier@gmail.com, elliot@townx.org, Jeremy Kemper]
+
 * Deprecate the old, confusing :exclusively_dependent option in favor of :dependent => :delete_all.  [Jeremy Kemper]
 
 * More compatible Oracle column reflection.  #2771 [Ryan Davis <ryand-ruby@zenspider.com>, Michael Schoen <schoenm@earthlink.net>]

activerecord/lib/active_record/associations.rb

@@ -652,8 +652,17 @@ def has_and_belongs_to_many(association_id, options = {}, &extension)
       
         collection_accessor_methods(association_name, association_class_name, association_class_primary_key_name, options, HasAndBelongsToManyAssociation)
 
-        before_destroy_sql = "DELETE FROM #{options[:join_table]} WHERE #{association_class_primary_key_name} = \\\#{self.quoted_id}"
-        module_eval(%{before_destroy "self.connection.delete(%{#{before_destroy_sql}})"}) # "
+        # Don't use a before_destroy callback since users' before_destroy
+        # callbacks will be executed after the association is wiped out.
+        old_method = "destroy_without_habtm_shim_for_#{association_name}"
+        class_eval <<-end_eval
+          alias_method :#{old_method}, :destroy_without_callbacks
+          def destroy_without_callbacks
+            #{association_name}.clear
+            #{old_method}
+          end
+        end_eval
+
         add_association_callbacks(association_name, options)
         
         # deprecated api

activerecord/test/associations_test.rb

@@ -1246,10 +1246,13 @@ def test_deleting_all
   end
 
   def test_removing_associations_on_destroy
-    Developer.find(1).destroy
-    assert Developer.connection.select_all("SELECT * FROM developers_projects WHERE developer_id = 1").empty?
+    david = DeveloperWithBeforeDestroyRaise.find(1)
+    assert !david.projects.empty?
+    assert_nothing_raised { david.destroy }
+    assert david.projects.empty?
+    assert DeveloperWithBeforeDestroyRaise.connection.select_all("SELECT * FROM developers_projects WHERE developer_id = 1").empty?
   end
-  
+
   def test_additional_columns_from_join_table
     # SQL Server doesn't have a separate column type just for dates, 
     # so the time is in the string and incorrectly formatted

activerecord/test/fixtures/developer.rb

@@ -28,3 +28,13 @@ class DeveloperWithAggregate < ActiveRecord::Base
   self.table_name = 'developers'
   composed_of :salary, :class_name => 'DeveloperSalary', :mapping => [%w(salary amount)]
 end
+
+class DeveloperWithBeforeDestroyRaise < ActiveRecord::Base
+  self.table_name = 'developers'
+  has_and_belongs_to_many :projects, :join_table => 'developers_projects', :foreign_key => 'developer_id'
+  before_destroy :raise_if_projects_empty!
+
+  def raise_if_projects_empty!
+    raise if projects.empty?
+  end
+end