Count Vs Exists (ARCH2063)

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Key python.orm.count-vs-exists · Severity info · Category orm

Using count() > 0 to test for presence counts all rows; exists() stops at the first row and gives the same answer far more cheaply.

Incorrect

if User.objects.filter(email=email).count() > 0:
    raise ValueError("taken")  # needless full count

if User.objects.filter(email=email).exists():
    raise ValueError("taken")  # short-circuits at first row

Use the short-circuiting exists() instead of count() > 0 for presence checks.