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Require explicit ShowMandatory in the good sample, acknowledge that NotBlank marking is unreliable, and limit findings to visible editable controls on paths where users must supply a value. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 89dba8c8-6529-4b60-956f-875a59be499d
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Mark code-required page fields with ShowMandatory
Contributions welcome — open a PR to refine or extend this article.
Description
ShowMandatory draws the red asterisk on a page field and, per the platform documentation, enforces no validation. The reverse is not reliable: code that enforces a value — TestField in OnInsert/OnModify, a NotBlank table field, a mandatory setup value — does not guarantee that the page field renders as mandatory. Because the two halves are independent, it is easy to ship a field that the code requires but the UI presents as optional. Microsoft documents that NotBlank can mark primary-key fields, but current client behavior does not do so consistently; on non-primary-key fields, a value that was never entered is not validated at all. ShowMandatory also overrides any marking NotBlank would contribute, so set it explicitly when the page must communicate a requirement. The gap is widest on a list page with DelayedInsert = true, where the enforcing error surfaces only when the user leaves the row — after the rest of the line is typed, with nothing having indicated which field was missing.
Best Practice
Set ShowMandatory = true on every visible, editable page field whose value the user must supply before the record can be committed or an action can complete, and leave the enforcement in place: the property is presentation, TestField/Error is the guarantee, and the two belong together in the same change. When the requirement is conditional, bind ShowMandatory to a Boolean variable or field that mirrors the condition the enforcement checks — the base application drives Vendor Invoice No. on the Purchase Invoice page from an Ext. Doc. No. Mandatory setup flag this way. Two expression limits are worth knowing: the property cannot call an AL method, so compute the value into a variable first, and a numeric field that has a default value counts as filled, so it never shows the asterisk. See sample: showmandatory-on-code-required-page-fields.good.al.
Anti Pattern
A required field with no mandatory marker: the table's OnInsert or the page's OnInsertRecord calls TestField on a field, or NotBlank is expected to force entry, while the page field bound to it carries no ShowMandatory. On a DelayedInsert = true list page the user fills the row, leaves it, and gets an error naming a field that never looked different from the optional ones. Reviewer signal: code on the relevant commit or action path requires the user to supply a field, the corresponding page control is visible and editable, and its ShowMandatory property is missing or does not mirror the same condition. A TestField or Error elsewhere in OnValidate or OnModify is not sufficient evidence: the field may be populated by code, non-editable, or required only for another path. Setting ShowMandatory = false on a field that is unconditionally required on the current path is the same defect stated explicitly, and per the documentation it also overrides any marking NotBlank would otherwise contribute. See sample: showmandatory-on-code-required-page-fields.bad.al.
See also
ShowMandatory property — https://learn.microsoft.com/dynamics365/business-central/dev-itpro/developer/properties/devenv-showmandatory-property
NotBlank property — https://learn.microsoft.com/dynamics365/business-central/dev-itpro/developer/properties/devenv-notblank-property
Review finding this article generalizes — https://github.com/microsoft/BCApps/pull/9315#discussion_r3568817946