bcquality/microsoft/knowledge/performance/avoid-calcfields-in-loops.md
Jesper Schulz-Wedde 62dabf9a11 Co-locate AL samples next to their knowledge articles
The /samples/ top-level tree is replaced with sibling files in each
knowledge-layer folder. An article and its demonstrations now live
side-by-side:

  microsoft/knowledge/<domain>/<slug>.md
  microsoft/knowledge/<domain>/<slug>.good.al
  microsoft/knowledge/<domain>/<slug>.bad.al

Rationale:
- Proximity. An article and its paired samples are one unit; the
  filesystem now reflects that.
- Layer ownership. Samples inherit layer precedence for free -- a
  /custom/ fork can override an article and its samples atomically,
  which the shared /samples/ tree previously made awkward.
- Trivial migration path. Action-skill source globs
  (*/knowledge/<domain>/**/*.md) are unchanged; sample discovery is a
  sibling-filename lookup.

Changes:
- git mv of all 65 sample files from samples/<domain>/<slug>/{bad,good}.al
  to microsoft/knowledge/<domain>/<slug>.{bad,good}.al (history preserved).
- Update See-sample references in all 37 articles that ship samples.
- skills/read.md: replace the no-code-blocks bullet with a pointer to a
  new Sample files section that fully specifies the sibling convention,
  the kinds (good/bad + forward-compatible), multi-technology rules,
  demonstration-only status, and layer-precedence behaviour.
- skills/write.md: update the samples pointer to match.
- README.md: annotate the knowledge tree with the sample sibling shape.
- samples/README.md deleted; content lifted into skills/read.md.
- Both generators (C:\temp\gen_performance_knowledge.py,
  C:\temp\gen_security_knowledge.py) updated to emit at the new paths
  and to stop writing samples/README.md. Re-running them is idempotent
  against the committed layout.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
2026-04-17 13:45:33 +02:00

1.3 KiB

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

Seed article. Converted from an existing performance-review prompt to bootstrap the BCQuality performance corpus. Domain stewards should expand, restructure, and refine as needed.

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.