increment_positions_on_lower_items called twice on insert_at with new item

[demery]

I found unexpected behavior when I call insert_at(position) on a new item (as is shown in the test_list.rb in the gem). If I insert a newly created (and not yet saved object), increment_positions_on_lower_items gets called twice, so that given positions [1,2], new_object.insert_at(2) results in positions [1,2,4].

See the following:

## GET THE PARENT
ruby-1.9.2-p290 :030 > shoot_list = ShootList.first
  ShootList Load (0.6ms)  SELECT "shoot_lists".* FROM "shoot_lists" LIMIT 1
 => #<ShootList id: 1, name: "xyx", manuscript_id: 1, lighting_config_id: nil, imaging_setup_id: nil, imaging_mode: nil, imaging_system_id: nil, created_at: "2011-11-11 22:26:39", updated_at: "2011-11-11 22:26:39"> 

### TWO ORDERED CHILDREN IN THE LIST
ruby-1.9.2-p290 :031 > shoot_list.shot_sequences.map(&:position)
  ShotSequence Load (0.7ms)  SELECT "shot_sequences".* FROM "shot_sequences" WHERE "shot_sequences"."shoot_list_id" = 1 ORDER BY position
 => [1, 2] 

## CREATE A NEW CHILD AND INSERT IT
ruby-1.9.2-p290 :032 > shot_sequence = ShotSequence.new(:subject => "elephant", :shoot_list => shoot_list)
 => #<ShotSequence id: nil, operator_instructions: nil, subject: "elephant", rotation_degrees: 0, position: nil, created_at: nil, updated_at: nil, shoot_list_id: 1> 
ruby-1.9.2-p290 :033 > shot_sequence.insert_at(2)
  SQL (2.2ms)  UPDATE "shot_sequences" SET position = (position + 1) WHERE ("shot_sequences"."shoot_list_id" = 1 AND position >= 2)
   (0.1ms)  BEGIN
  SQL (0.4ms)  UPDATE "shot_sequences" SET position = (position + 1) WHERE ("shot_sequences"."shoot_list_id" = 1 AND position >= 2)
  SQL (0.7ms)  INSERT INTO "shot_sequences" ("created_at", "operator_instructions", "position", "rotation_degrees", "shoot_list_id", "subject", "updated_at") VALUES ($1, $2, $3, $4, $5, $6, $7) RETURNING "id"  [["created_at", Mon, 14 Nov 2011 12:34:05 EST -05:00], ["operator_instructions", nil], ["position", 2], ["rotation_degrees", 0], ["shoot_list_id", 1], ["subject", "elephant"], ["updated_at", Mon, 14 Nov 2011 12:34:05 EST -05:00]]
   (0.4ms)  COMMIT
 => true 

### RELOAD THE PARENT AND LIST THE CHILDREN
ruby-1.9.2-p290 :035 > shoot_list = ShootList.first
  ShootList Load (0.6ms)  SELECT "shoot_lists".* FROM "shoot_lists" LIMIT 1
 => #<ShootList id: 1, name: "xyx", manuscript_id: 1, lighting_config_id: nil, imaging_setup_id: nil, imaging_mode: nil, imaging_system_id: nil, created_at: "2011-11-11 22:26:39", updated_at: "2011-11-11 22:26:39"> 
ruby-1.9.2-p290 :036 > shoot_list.shot_sequences.map(&:position)
  ShotSequence Load (0.8ms)  SELECT "shot_sequences".* FROM "shot_sequences" WHERE "shot_sequences"."shoot_list_id" = 1 ORDER BY position
 => [1, 2, 4] 
ruby-1.9.2-p290 :037 > 

Note that two update calls are made to do the position increment. I stuck a backtrace printout in increment_positions_on_lower_items(position) and found the first call was made on insert and the second when the before_create callback is made.

Creating the item, and then inserting it in the correct position gets the desired result.

[swanandp]

Hmm.. this is indeed weird. I have a feeling this was introduced during one of the recent pull requests. I am looking into this now, thanks for reporting!

[swanandp]

The test test_insert_middle_with_unsaved_item addresses this issue and I think its fixed in the latest version. Can you please verify that it works for you?
Note: The latest version is not pushed to Rubygems yet.

[swanandp]

This commit: f5bbea4