bcquality/microsoft/knowledge/upgrade/guard-database-reads.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

26 lines
1.3 KiB
Markdown

---
bc-version: [all]
domain: upgrade
keywords: [get, findset, findlast, guard, if-then, runtime-error]
technologies: [al]
countries: [w1]
application-area: [all]
---
# Guard every database read in upgrade code with `if`
## Description
Inside an upgrade codeunit (or any procedure transitively invoked from `OnUpgradePerCompany` / `OnUpgradePerDatabase`), an unguarded `Record.Get`, `Record.FindSet`, or `Record.FindLast` raises a runtime error when the row or set is missing. In upgrade context that error aborts the entire upgrade for the company or database — a far worse outcome than the missing data itself. Records the upgrade reasons about may legitimately not exist on every customer's tenant.
## Best Practice
Wrap every read in an `if`. `if Item.Get(No) then ...`, `if Customer.FindSet() then;`, `if not Vendor.FindLast() then exit;`. The empty-then form `if Customer.FindSet() then;` is the idiomatic way to attempt a read whose only purpose is to position a record, while swallowing the "not found" case.
See sample: `guard-database-reads.good.al`.
## Anti Pattern
Calling `Item.Get()`, `Customer.FindSet()`, or `Vendor.FindLast()` bare in upgrade code. The first tenant whose data does not match the upgrade's assumptions will fail to upgrade.
See sample: `guard-database-reads.bad.al`.