Unable to delete a parent with dependent destroy

[onerinas]

I'm seeing below error when deleting a parent model which has dependent destroy

undefined method `+' for nil ["/Users/rinas/.asdf/installs/ruby/3.3.0/lib/ruby/gems/3.3.0/gems/positioning-0.2.6/lib/positioning/mechanisms.rb:43:in `destroy_position'",

e.g,

class TodoList
  has_many :todos, dependent: :destroy
end


class Todo
  # has_ancestry cache_depth: true, counter_cache: true, primary_key_format: "[-A-Fa-f0-9]{36}"

  belongs_to :todo_list
  belongs_to :todo_list_version

  # positioned on: [:todo_list, :todo_list_version, :ancestry]
  positioned on: [:todo_list]
end

Error occurs when I do todo_list.destroy which has multiple todos and has position. I have commented out few lines to add some context. I don't think that's the reason but still keeping it in case it's helpful.

I'm on on 0.2.6. Any other details I can add that might help find what's happening?

[onerinas]

Tested in latest 0.4.5:

undefined method `+' for nil ["/Users/rinas/.asdf/installs/ruby/3.3.0/lib/ruby/gems/3.3.0/gems/positioning-0.4.5/lib/positioning/mechanisms.rb:49:in `destroy_position'",

[onerinas]

@brendon Is it because of multiple scopes?

Looking at

positioning/lib/positioning/mechanisms.rb

Line 227 in 4ce54e4

@positioned.destroyed_by_association.foreign_key == scope_column

we are comparing
@positioned.destroyed_by_association.foreign_key == scope_column

Could that be the reason?

[brendon]

Hi @onerinas, that's an interesting one. It appears to be failing to detect that it's being deleted via a scope.

It shouldn't matter but try not passing in an array:

positioned on: :todo_list

Here's the current test for this scenario:

positioning/test/test_positioning.rb

Lines 568 to 582 in 4ce54e4

	def test_destroyed_via_positioning_scope?
	list = List.create name: "List"
	student = list.authors.create name: "Student", type: "Author::Student"
	teacher = list.authors.create name: "Teacher", type: "Author::Teacher"
	mechanisms = Positioning::Mechanisms.new(student, :position)
	refute mechanisms.send(:destroyed_via_positioning_scope?)
	mechanisms = Positioning::Mechanisms.new(teacher, :position)
	teacher.destroy
	refute mechanisms.send(:destroyed_via_positioning_scope?)
	list.destroy
	assert mechanisms.send(:destroyed_via_positioning_scope?)
	end

If you feel up to it, can you try to recreate the issue with a test and then create a PR with that failing test and I'll see what I can find.

What version or Rails are you on?

[onerinas]

@brendon In my actual code, I have more than one column used and hence the array like this:

positioned on: [:todo_list, :todo_list_version, :ancestry]

I’ll try to add a test to see if it fails. I hope that would be helpful.

[brendon]

It’ll definitely be helpful. Is your parent model double linked to the child with two dependent: destroys?