Worked on the ash-project/ash repository to deliver a Bulk Create Upsert enhancement focused on preserving update_default fields during upsert operations. Developed in Elixir, this feature introduced the touch_update_defaults option, allowing explicit control over whether fields like updated_at are modified during bulk and non-bulk upserts. The implementation spanned both ETS and Mnesia data layers, ensuring consistent behavior across storage backends. By wiring the option through Ash.create! and leveraging data-layer callbacks and changeset context, the work improved data integrity and enabled safer bulk operations, particularly during data migrations. The effort demonstrated depth in backend development and data layer management.