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Your Django REST Framework Serializer Is Making 200 Database Queries Per Request
The queries aren’t in your view. They’re in your serializer.
We had an API endpoint that returned a list of 25 orders. The view was clean — one queryset, one serializer, paginated. In development, it responded in 180 milliseconds. In production, with real data and relationships, it took 4.7 seconds.
I opened django-debug-toolbar on the browsable API. 214 queries. For 25 orders.
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The view had select_related('customer'). The obvious N+1 was covered. But the serializer had a SerializerMethodField that accessed order.items.all(). Another nested serializer pulled item.product.category. A StringRelatedField on the product called __str__(), which accessed product.brand.name. Every one of these was a lazy load. Every lazy load fired a query. For every row.
25 orders × 4 items each × 2 lazy lookups per item = 200+ queries, generated entirely inside the serializer — invisible from the view.
The serializer wasn’t slow. The serializer was making the ORM do work the view never…
