bcquality/microsoft/knowledge/privacy/avoid-strsubstno-prebuild-before-error.md
Jesper Schulz-Wedde a9f3c50863 Regenerate microsoft/knowledge from upstream BCApps instructions
The previous LLM-generated knowledge files contained factual
hallucinations. The most visible was the claim that `FindFirst` /
`FindLast` "forces a full-table scan" on an unfiltered record - it does
not; those APIs return a single row via the current key.

Other inaccuracies the audit found and fixed:

* `FindSet(true)` was described as "taking a LockTable". The correct
  upstream phrasing is that `FindSet(true)` sets
  `ReadIsolation::UpdLock` on the read. UpdLock and LockTable are
  related but distinct mechanisms.
* The list of production-scale tables had been invented beyond the
  upstream source (e.g. "Detailed Cust. Ledg. Entry") without a
  citation. The regenerated list matches the ten tables upstream lists
  with their P95 row counts.
* `SetLoadFields` guidance had been augmented with an extra mechanism
  claim ("the database resolves the filter using the index without
  hydrating the value") not present in upstream.

Approach: full regeneration of `microsoft/knowledge/` from the six
upstream BCApps Code Review instruction files, with Microsoft Learn /
the AL language reference as a secondary source. Every claim in every
regenerated file is anchored to a verbatim upstream quote (or a Learn
URL); the audit trail lives in artifacts/trace-<domain>.json on the
session workspace.

The PR #11 transaction/error-handling cluster is preserved verbatim:

* performance/understand-implicit-transaction-boundary.md
* performance/codeunit-run-as-atomic-sub-operation.{md,good.al,bad.al}
* performance/codeunit-run-requires-prior-commit-inside-transaction.{md,good.al,bad.al}
* performance/use-tryfunction-for-error-catching-not-rollback.{md,good.al,bad.al}
* performance/avoid-commit-inside-loops.{md,good.al,bad.al}
* security/commitbehavior-attribute-scopes-explicit-commits.{md,good.al,bad.al}
* testing/transactionmodel-attribute-governs-test-transactions.{md,good.al,bad.al}

These articles already cite Microsoft Learn and were carefully
cross-referenced; the regeneration skips their topics rather than
duplicating them.

File counts after regeneration:

  performance   35 .md  (5 preserved + 30 new)
  privacy       17 .md
  security      18 .md  (1 preserved + 17 new)
  style         33 .md
  testing        1 .md  (preserved)
  ui            19 .md
  upgrade       18 .md

Total 141 atomic knowledge files, each strictly one rule. All pass
.github/scripts/validate_frontmatter.py with 0 errors and 0 warnings.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
2026-05-21 09:53:09 +02:00

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1.7 KiB
Markdown

---
bc-version: [all]
domain: privacy
keywords: [strsubstno, error, telemetry, pii, prebuild, text-variable]
technologies: [al]
countries: [w1]
application-area: [all]
---
# Do not pre-build an error string with `StrSubstNo` before calling `Error()`
## Description
`StrSubstNo` returns a plain `Text` value with the substitutions already performed. When that result is then passed to `Error()`, the platform sees a single plain-text parameter with no field references left to inspect, so it cannot apply `DataClassification` to anything inside it. Whatever PII the `StrSubstNo` call interpolated — customer name, e-mail, address, error text — is logged verbatim to telemetry. This is the canonical way to accidentally leak customer data through error telemetry, and it is the only `Error()` shape that needs to be flagged.
## Best Practice
Call `Error()` directly with the format string and the substitution parameters. The platform classifies each parameter individually and handles telemetry correctly even when the parameters are PII fields (see `error-direct-substitution-safe-for-telemetry.md`). If the message text needs to be a `Label`, pass the `Label` and the parameters to `Error()` — do not pre-render via `StrSubstNo`.
See sample: `avoid-strsubstno-prebuild-before-error.good.al`.
## Anti Pattern
Assigning `StrSubstNo('Customer %1 (%2) ...', Customer.Name, Customer."E-Mail")` to a `Text` variable and then calling `Error(ErrorMsg)`. The platform has nothing to classify by the time `Error` runs — the PII is baked into the string and goes straight to telemetry. Detection signal for a reviewer: any `Text` variable assigned from `StrSubstNo` and later passed as the *only* parameter to `Error()`.
See sample: `avoid-strsubstno-prebuild-before-error.bad.al`.