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

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Markdown

---
bc-version: [26..28]
domain: performance
keywords: [calcfields, flowfield, loop, n-plus-one]
technologies: [al]
countries: [w1]
application-area: [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`.