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bcquality/microsoft/knowledge/performance/avoid-calcfields-in-loops.md
Jesper Schulz-Wedde 23184480d0 Triage seed knowledge and document admission test for preview 
Remove seven knowledge files whose content is generic software-engineering
guidance that a capable LLM already applies without BCQuality present
(HTTPS-only, secret-leakage-in-errors, no-credentials-in-URLs, silent
security-error swallowing, short transaction scope, HTTP timeouts,
StrSubstNo-vs-concatenation). These fail the remedial-knowledge premise
and dilute the signal of the preview corpus.

Strip the "Seed article — domain stewards should expand" banner from ten
files that are ready to showcase (AA0232/AA0233 rules, FindSet read-only
semantics, SetLoadFields ordering and usage, CalcFields-in-loops,
SecretText end-to-end, DataClassification). The banner remains on files
that still need domain-steward refinement.

Add a "What belongs here" section to the README stating the admission
test: a file exists only if a modern LLM would get something wrong or
miss something without it. Gives contributors a concrete yes/no filter
before they open a PR.
2026-04-23 15:47:01 +02:00

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bc-version domain keywords technologies countries application-area
26..28
performance
calcfields
flowfield
loop
n-plus-one
al
w1
all

Do not call CalcFields inside loops

Description

CalcFields evaluates one or more FlowFields for the current record by issuing a separate SQL aggregation. Called inside a loop over a record set, it becomes an N+1 problem: one aggregate per row. For any non-trivial set on a ledger-entry-backed FlowField this is orders of magnitude slower than the equivalent batched query.

Best Practice

Move CalcFields out of the iteration. If the total is what you need, use CalcSums on the filtered parent set. If row-by-row FlowField values are needed, reshape the computation so the aggregate runs once — for example by joining against a temporary table populated in a single batched query.

See sample: avoid-calcfields-in-loops.good.al.

Anti Pattern

Calling CalcFields inside repeat ... until Next() = 0 on a hot parent record is the textbook N+1 pattern. Even a modest parent set size (hundreds of rows) turns into thousands of round-trips.

See sample: avoid-calcfields-in-loops.bad.al.