Delete foreign_constraint on has_many

Questions / Help
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1

I faced with very similar problem as @grufino in his topic regarding the foreign key on nested models deletion.

I prepared a small sample code to show the problem.

I did exactly the same as written in the topic above and manually added changeset foreign_key_constraint/3 on changed has_many model since in Relation.ex file in Ecto has a such code {:ok, Changeset.change(changeset_or_struct) |> put_new_action(:replace)} which doesn’t take any parameter to pass deletion changeset and always raises foreign_key exception.

The current test looks like

  test "delete foreign key test", %{user_id: user_id} do
    timetable = insert(:timetable, %{
      user_id: user_id,
      date_ranges: [
        build(:today_date_range, %{
          slots: [
            build(:now_date_range_slot)
          ]
        })
      ]
    })
    # Create foreign model to raise a FK exception.
    _check = insert(:check, %{
      date_range_id: List.first(timetable.date_ranges).id,
      date_range_id: List.first(List.first(timetable.date_ranges).slots).id,
      user_id: user_id
    })

    update_attrs = string_params_for(:timetable, %{
      date_ranges: [
        build(:tomorrow_date_range, %{
          slots: [
            build(:now_date_range_slot)
          ]
        })
      ]
    })

    assert {:error, %Ecto.Changeset{} = changeset} = EctoDelete.TimetableManager.update_timetable(timetable, update_attrs)
    assert errors_on(changeset) == %{}
  end

And the output is

  1) test delete foreign key test (EctoForeignDeleteAppTest)
     test/ecto_foreign_delete_app_test.exs:12
     Assertion with == failed
     code:  assert errors_on(changeset) == %{}
     left:  %{date_ranges: [%{timetable: ["You can't delete this date range. You have checks"]}, %{}]}
     right: %{}
     stacktrace:
       test/ecto_foreign_delete_app_test.exs:42: (test)

The exception is gone and now I have this beautiful error. But as you can see date_ranges has an empty %{} in the list, so when call Ecto.Changeset.traverse_errors it is considers inserted/updated schemas as affected, but they are not and shouldn’t have this map inside. The same is applicable on slot deletion(means next nesting level)

Any suggestions?