bcquality/microsoft/knowledge/data-modeling/table-relation-extensions-are-additive-and-top-down.md
Jesper Schulz-Wedde 186d8a1314
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Complete AL review knowledge readiness (#108)
* Complete AL review knowledge readiness

Fill telemetry and Query coverage, strengthen thin review domains, correct audited content defects, and add deterministic cheap-model evaluation and reference-integrity safeguards.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 9825b012-e653-496a-9310-c1f4b6f8ac27

* Generalize review fixture discovery

Derive smoke cases from the leaf, domain, and paired-sample conventions so new leaves require no scoring-contract changes. Keep only exceptional selection/context overrides and fail when retrieval metadata cannot rank the selected article.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 9825b012-e653-496a-9310-c1f4b6f8ac27

* Preserve published field IDs in sample

Keep the existing Email and Contact Email field IDs unchanged, clarify that the sample represents an independent baseline, and use a local breaking-change rule for the generic smoke evaluation.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 9825b012-e653-496a-9310-c1f4b6f8ac27

* Clarify published field identity rules

State explicitly that a published field keeps its ID, name, and type while a replacement is added as a separate field under an unused ID.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 9825b012-e653-496a-9310-c1f4b6f8ac27

* Align field obsoletion sample baselines

Use Email field ID 3 as the shared baseline so the bad example demonstrates a same-ID rename while the good example retains the original field and adds a separate replacement.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 9825b012-e653-496a-9310-c1f4b6f8ac27

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Co-authored-by: Jesper Schulz-Wedde <jesper.schulzwedde@microsoft.com>
2026-07-15 10:55:25 +02:00

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---
bc-version: [all]
domain: data-modeling
keywords: [tablerelation, tableextension, enumextension, additive, top-down, unconditional-relation]
technologies: [al]
countries: [w1]
application-area: [all]
---
# Design TableRelation branches for additive top-down extension
## Description
A `tableextension` can add to an existing `TableRelation`, but the combined relation is evaluated top-down after the original value. The first unconditional relation wins. An extension branch appended after an unconditional base relation is therefore unreachable, even though the extension compiles and appears to describe the new enum value correctly.
## Best Practice
When a relation is designed to follow an extensible enum, express the base cases as conditional branches and leave no unconditional catch-all ahead of future extension branches. An enum extension can then append a condition for its new value. When extending a field you do not own, inspect the original `TableRelation`; do not claim that an appended condition overrides an unconditional relation.
See sample: `table-relation-extensions-are-additive-and-top-down.good.al`.
## Anti Pattern
A base field has an unconditional `TableRelation = Customer;` and a `tableextension` adds `if (Type = const(Resource)) Resource`. The original unconditional branch always wins, so the new enum value still validates and looks up against Customer. The concern is evaluation order, not `ValidateTableRelation`; free-form input is covered separately by security guidance.
See sample: `table-relation-extensions-are-additive-and-top-down.bad.al`.