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Three related concerns, each proven by executable tests rather than recall. They were extracted from a real defect that shipped through a six-reviewer panel undetected, which is the admission test passing on behavior rather than on theory. owning-table-must-delete-dependents-in-ondelete AL has no cascading delete. What makes it missable is an asymmetry: the platform DOES keep references correct on rename via TableRelation, so a developer who learns that and generalizes it to delete ships orphans. Also notes the permission trap (delete rights needed on the dependent table, not just the parent). validate-table-relation-false-suppresses-rename-propagation The non-obvious half. The property name implies input validation only, but disabling it also switches off rename propagation. Verified against a parent renamed once while a child held three fields: a normal relation (follows), the same relation with validation disabled (does NOT follow), and a field with no relation at all (does not follow) — the third being the control that proves the test can detect a non-propagating field. xrec-is-a-before-image-only-in-some-triggers Corrects both the naive belief that xRec is always the previous record and the folk rule that it 'only works from a page'. The behavior is per-trigger: a genuine before-image in OnRename and OnDelete regardless of driver, a mirror of Rec in OnInsert/OnModify when driven from code, and a real before-image in those two only when a page drove the write. That last asymmetry is why an OnModify comparison against xRec passes manual page testing and silently no-ops in a job queue. Targets /community per CONTRIBUTING — general BC knowledge, not fork-specific. Frontmatter validator clean; Test-ReviewFixtures passes (32 cases, 16 leaves).
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A table that owns dependent records must delete them in OnDelete
Description
TableRelation looks like referential integrity but only performs lookup and input validation. AL has no cascading delete: deleting a parent record leaves every dependent row untouched, and no error is raised.
What makes this specifically missable is an asymmetry. The platform does keep references correct on rename — renaming a record updates it in all other locations that declare a TableRelation to it, with no code. Delete has no equivalent. Same relation, same metadata, opposite behaviour. A developer who correctly learns that TableRelation "keeps references consistent" from the rename case, and generalises it to delete, ships orphans.
Orphaned rows are usually invisible, because a dependent table rarely has a page of its own. They inflate the table, break later reconciliation, and are re-encountered by duplicate checks when the parent key is reused.
This applies to internal, staging and SystemMetadata tables too. A table having no delete action in the UI today is not protection: a permission set that grants D on the table is evidence that deletion is anticipated.
See also validate-table-relation-false-suppresses-rename-propagation.md for the two preconditions on the rename half of this asymmetry.
Best Practice
The owning table implements OnDelete and deletes its dependents there, filtered on the foreign key. Declare Permissions = tabledata <dependent> = rd on the owning table — granting delete rights only on the parent is a common miss that makes the trigger fail for a non-SUPER user. This mirrors the base application, where every header table deletes its own lines.
See sample: owning-table-must-delete-dependents-in-ondelete.good.al.
Anti Pattern
A parent table with dependent rows and no OnDelete trigger, where the dependent's foreign-key field declares a TableRelation back to the parent. The relation reads as if it guarantees integrity; it does not.
Detection signal: a table declares TableRelation to table X, and table X has no OnDelete trigger. Whether a delete path currently exists in the UI is irrelevant to the finding.
See sample: owning-table-must-delete-dependents-in-ondelete.bad.al.