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bcquality/microsoft/knowledge/performance/isempty-before-findset-is-extra-round-trip.md
Jesper Schulz-Wedde 42ff075793 Promote knowledge for Microsoft review skills 
Move canonical knowledge for Microsoft-owned review domains into the Microsoft layer and document the skill/knowledge co-location policy.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 2a6ea875-d38e-4f30-aadb-0d606f9be231
2026-09-03 14:59:44 +02:00

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bc-version domain keywords technologies countries application-area
all
performance
isempty
findset
extra-round-trip
existence-check
false-positive
al
w1
all

IsEmpty immediately before FindSet is an extra round-trip

Contributions welcome — open a PR to refine or extend this article.

Description

IsEmpty is the right API when the caller only needs existence — see microsoft/knowledge/performance/use-isempty-for-existence-check.md. It is not a cheap guard in front of a loop that will FindSet anyway. Both calls hit the database; FindSet already returns false when the filter matches nothing. Agents and reviewers often insert if not Rec.IsEmpty() then "for performance" and pay a second query for a result the iterator already provides.

Best Practice

When the body iterates, open with if Rec.FindSet() then repeat ... until Next() = 0. Do not flag a bare FindSet loop as missing an IsEmpty precondition. Reserve IsEmpty for branches that never materialize the row set.

See sample: isempty-before-findset-is-extra-round-trip.good.al.

Anti Pattern

if not Rec.IsEmpty() then if Rec.FindSet() then repeat. Also a false-positive review comment that asks to add that guard. The second read does not avoid the first; it duplicates it.

See sample: isempty-before-findset-is-extra-round-trip.bad.al.