bcquality/microsoft/knowledge/performance/do-not-modify-records-in-onaftergetrecord.md
Jesper Schulz-Wedde e570d6113f Extract 55 knowledge articles from BC review-agent prompt
Adds 55 articles (plus 76 code samples) spanning four new domains and
two existing domains, extracted from the internal Business Central
review-agent prompt. Content was filtered against BCQuality's
remedial-knowledge premise: each article encodes BC-specific behaviour,
a CodeCop rule, a platform API semantic, or an anti-false-positive
guideline that a capable LLM would otherwise get wrong.

New domains:
- privacy (11 articles): DataClassification inheritance semantics, the
  StrSubstNo-defeats-Error-telemetry-classification pitfall, Privacy
  Notice consent for outgoing requests, anti-false-positives for pages
  and in-memory data.
- upgrade (11 articles): upgrade-codeunit structure, upgrade-tag
  lifecycle and registration, protected DB reads, DataTransfer for
  large datasets, InitValue semantics, enum-ordinal preservation,
  obsolete-workflow, first-install detection.
- ui (9 articles): caption capitalization by phrase type, tooltip voice,
  teaching-tip vs tooltip, tour-tip conventions, character limits,
  banned terms, ampersand handling, title punctuation.
- style (11 articles): label-suffix convention, API page naming,
  temporary-variable prefix, label properties (Comment/Locked), named
  invocations, FieldCaption in user messages, OptionCaption pairing,
  Error-parameter passing, `this` keyword, required parentheses, file
  naming.

Gaps in existing domains:
- performance (11 articles): production-scale table catalog (no row
  counts, per internal-data concern), anti-false-positive for bounded
  tables, guard-before-Get ordering, redundant-Get-in-OnAfterGetRecord,
  LockTable in read-only helpers, combined ModifyAll passes, writes in
  OnAfterGetRecord, SetLoadFields heuristics, temporary-table
  regressions, FlowField source-table widening, MaintainSQLIndex
  disabling SIFT.
- security (2 articles): environment-specific hardcoded GUIDs,
  ValidateTableRelation=false on user input.

Intentionally excluded: specific production P95 row-count numbers
(aggregated internal telemetry); rewritten as categorical guidance on
which tables to treat as production-scale without publishing sizes.

All articles use `bc-version: [all]` (applies to every BC version, per
the new schema sentinel). Validator passes with 0 errors / 0 warnings.
2026-04-23 16:43:42 +02:00

1.6 KiB

bc-version domain keywords technologies countries application-area
all
performance
onaftergetrecord
modify
page
trigger
write-per-scroll
al
w1
all

Do not Modify records inside OnAfterGetRecord

Description

OnAfterGetRecord fires for every row the page or repeater renders. On a list page the user scrolls through, the trigger runs hundreds of times per second. A Modify() call inside the trigger writes to the database for every row scrolled past — the user's mouse wheel generates the write storm, and the effect compounds with every other subscriber that reacts to the OnModify event. The database activity is usually invisible to the author in development, because the list page loads ten rows; on a production tenant scrolling through thousands of rows, the page becomes the top source of write volume.

Best Practice

Derive display-only state into a page-level variable and bind that variable to the field control instead of writing to Rec. If the computed value is genuinely a stored attribute of the record, compute it once at the authoring site (OnValidate, OnInsert) and display the stored value on the list — do not recompute and rewrite on every render.

See sample: do-not-modify-records-in-onaftergetrecord.good.al.

Anti Pattern

An OnAfterGetRecord body that assigns a computed value to Rec."Warning Flag" and calls Rec.Modify() so the flag persists. The write fires per scroll, per user, per second — and every subscriber on the Rec's OnModify fires alongside.

See sample: do-not-modify-records-in-onaftergetrecord.bad.al.