Django ORM Query Optimization

Use this skill for query-count and object-loading problems. The usual target is an N+1 pattern where each rendered row or serialized object triggers more database work.

Workflow

1. Prove the query pattern.

   • Capture query count and duplicate SQL for the slow path.
   • Identify the loop, serializer field, template access, admin display, or model property triggering related queries.

2. Choose the loading strategy.

   • Use select_related() for single-valued relationships: ForeignKey and OneToOneField.
   • Use prefetch_related() for many-valued relationships: reverse FK and many-to-many.
   • Use Prefetch() when the related queryset needs filters, ordering, annotations, or nested select_related().
   • Use values() or values_list() when model instances are unnecessary.
   • Use only() or defer() only when large columns are truly unused.