bcquality/microsoft/knowledge/performance/runmodal-is-not-allowed-inside-write-transactions.md

bc-version	domain	keywords	technologies	countries	application-area
all	performance	runmodal page-runmodal report-runmodal xmlport-runmodal write-transaction commit requestpage runtime-error	al	w1	all

RunModal is not allowed inside a write transaction

Description

Once AL code has written to the database in the current transaction — an Insert, Modify, or Delete with no Commit since — the platform refuses to open a modal object until that transaction is committed. Page.RunModal fails unconditionally. Report.RunModal and XmlPort.RunModal fail when they would show a request page; with it suppressed — Report.RunModal(ReportId, false), where the second argument is RequestWindow, or UseRequestPage(false) on a report instance — they are allowed. Codeunit.Run fails when its Boolean return value is used (if Codeunit.Run() then), because that form commits — see codeunit-run-requires-prior-commit-inside-transaction.md. This is a runtime error, not a compiler diagnostic: the code builds, and the first execution that reaches the call with an open write transaction dies. The guard keys on transaction state alone, not on any relation between what was written and what is opened: an Item.Insert() followed by Page.RunModal(Page::"Customer Card") — an unrelated table — fails on the RunModal line, and because the error stops the transaction, the insert rolls back with it.

The platform's message (Business Central 26, reproduced 2026-09-07) reads: "The following AL methods are limited during write transactions because one or more tables will be locked: Form.RunModal, Codeunit.Run, Report.RunModal, XmlPort.RunModal. Form.RunModal is not allowed in write transactions. Codeunit.Run is allowed in write transactions only if the return value is not used. For example, 'OK := Codeunit.Run()' is not allowed. Report.RunModal is allowed in write transactions only if 'RequestForm = false'. For example, 'Report.RunModal(...,false)' is allowed. XmlPort.RunModal is allowed in write transactions only if 'RequestForm = false'. For example, 'XmlPort.RunModal(...,false)' is allowed. Use the commit method to save the changes before this call, or structure the code differently." The message still uses the legacy names Form.RunModal and RequestForm even though the AL method is Page.RunModal and the report parameter is RequestWindow; older versions said "C/AL functions" instead of "AL methods" (microsoft/AL#5452, 2019). The behavior is unchanged across versions.

The reason is the same one behind avoid-user-prompts-inside-transactions.md: a modal object waits for the user, and the platform will not let a write transaction — and every lock it holds — sit open for as long as that takes. The difference is enforcement. Confirm, StrMenu, and Message are allowed inside a write transaction and silently hold the locks; RunModal is refused. Both point at the same design fix.

Best Practice

Sequence the work so the modal interaction happens before the write phase: run the lookup or dialog page first, then perform the writes the user's choice requires, and let the transaction end. When a modal object genuinely must follow a write, Commit() first — but only when the state written so far is complete and safe to persist on its own, because that Commit is a real transaction boundary, not a formality. Microsoft's own Base Application follows exactly this pattern where the preceding state is final (ActivityLog.Table.al commits the log entry before Page.RunModal(Page::"Activity Log", Rec); DocumentSendingProfile.Table.al commits before Page.RunModal(Page::"Select Sending Options", …)). For a report or XMLport, suppressing the request page (UseRequestPage(false)) is a legitimate way to run it inside a write transaction when no user input is needed. Database.IsInWriteTransaction() (runtime 11.0+) lets library code that cannot control its caller detect the state, with the same caveat as the Codeunit.Run article: branching production flow on it usually signals unclear transaction ownership.

See sample: runmodal-is-not-allowed-inside-write-transactions.good.al.

Anti Pattern

Writing to the database and then calling Page.RunModal (or a report/XMLport with its request page) in the same trigger — the first production run hits the runtime error. The reflexive fixes are worse than the error: dropping in Commit() to silence it persists a half-finished state that can no longer roll back with the rest of the operation, and swapping the page for a Confirm or StrMenu to "avoid the error" trades a loud failure for the silent lock-holding that avoid-user-prompts-inside-transactions.md warns about.

See sample: runmodal-is-not-allowed-inside-write-transactions.bad.al.

Source

• Microsoft Learn, Codeunit.Run transaction semantics ("If you're already in a transaction you must commit first before calling Codeunit.Run"): https://learn.microsoft.com/dynamics365/business-central/dev-itpro/developer/methods-auto/codeunit/codeunit-run-method
• microsoft/AL issue #5452 (verbatim English error text, reproduced on "any current version of Business Central", 2019-11-13): https://github.com/microsoft/AL/issues/5452
• Reproduced 2026-09-07 on Business Central 26 (runtime error dialog, English and Danish clients): a page OnAction doing Item.Insert() then Page.RunModal(Page::"Customer Card") fails with the text quoted in the Description, the AL call stack pointing at the RunModal line, and the dialog stating that the transaction was stopped.
• Microsoft Base Application (BCApps, W1): the Commit(); … Page.RunModal(…) pattern in Modules/System/Logging/ActivityLog.Table.al, Foundation/Reporting/DocumentSendingProfile.Table.al, Bank/Setup/PaymentServiceSetup.Table.al, and others; BCApps test suites annotate the same guard as "COMMIT is required for Write Transaction Error" (Tests/General Journal/ERMTestMultipleGenJnlLines.Codeunit.al).