Query Inside Loop (ARCH2064)

Key python.orm.query-inside-loop · Severity warning · Category orm

Issuing any DB read query inside a loop body (an ad-hoc find, aggregate, or repository call) produces a round-trip per iteration. Hoist the query out of the loop.

Incorrect

for order in orders:
    customer = Customer.objects.get(id=order.customer_id)  # a query per iteration
    notify(customer)

Correct

ids = [o.customer_id for o in orders]
customers = {c.id: c for c in Customer.objects.filter(id__in=ids)}  # one query
for order in orders:
    notify(customers[order.customer_id])

Fix

Batch the in-loop queries into a single filter(id__in=...) and move it out of the loop.