ORM N+1 query (ARCH2079)

Key python.performance.orm-n-plus-one · Severity error · Category performance

Retired

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Looping over a query result and touching each item’s relation issues one extra query per row (N+1). Eager-load the relation with select_related/prefetch_related.

Incorrect

def list_authors():
    return [
        book.author.name
        for book in Book.objects.all()
    ]

Correct

def list_authors():
    return [
        book.author.name
        for book in Book.objects.select_related("author").all()
    ]

Fix

Eager-load related data in a single query with select_related or prefetch_related.