Bug: Possibly duplicated positions if not given `add_new_at: top` option

[Gee-Bee]

According to 0.8.0 Upgrade Notes:

If you specify add_new_at: :top, new items will be added to the top of the list like always. But now, if you specify a position at insert time: .create(position: 3), the position will be respected.

This works as expected, repositioning other items' positions if position is taken.

In my use case:

• I used add_new_at: nil (because position is optional),
• I allow specify position manually in create item form.

If user specify position that is already taken, DB is left in inconsistent state (or uniqueness constraint violation error is raised).

Expected result: reordering other items, like in add_new_at: :top scenario.

As a workaround I included the following concern in my class:

module ActsAsListCreateWithPositionFix
  extend ActiveSupport::Concern

  included do
    before_create -> { @_tmp_position = position and self.position = nil }
    after_create -> { insert_at(@_tmp_position) }, if: -> { @_tmp_position.present? }
  end
end

This workaround seems like a "bad example" from the 1) Use the Most Concise API in README:

# Good
TodoItem.create(todo_list: todo_list, position: 1)

# Bad
item = TodoItem.create(todo_list: todo_list)
item.insert_at(1)

but at least it works. The "Good example" generates possible duplicates when add_new_at: :top is not given.

[brendon]

Hi @Gee-Bee, I see what you mean. Would you be interested in creating a PR to fix this? I'll take a look too but am pretty short on time lately. If you have any ideas please let me know :)

[brendon]

Actually, I think I see a hopefully easy solution to the problem. I'll keep you posted.

[brendon]

Try https://github.com/brendon/acts_as_list/tree/avoid_collision to see if that helps. I've added tests that confirm it works.

[brendon]

Actually, since the tests are green I've merged it with master. Give master a go and see how you get on :)

[Gee-Bee]

Wow, that was fast. Tried master branch. It's working like a gold. You managed to resolve the issue and clean up the code along the way. Big props for your work.

[brendon]

Thanks @Gee-Bee! :) I'll spin a new release.