SharePoint custom form - How to prevent double booking of a room (overlapping start/end)?

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Posted on by MK-09020908-0

Hi everyone,

I’m building a SharePoint custom list form in Power Apps for booking meeting rooms.
The list has:
Salka (Room) – Choice field
Start – Date/Time
End – Date/Time

I need to prevent overlapping reservations for the same room (e.g., if an existing booking has Start < NewEnd AND End > NewStart).
I tried adding validation in SharePointIntegration.OnSave and also in a custom button’s OnSelect, but I keep getting formula errors or the check doesn’t work reliably in the SharePoint form integration.
What is the recommended way to validate overlapping bookings in a SharePoint custom form (Power Apps)?

Should this be done in the form (Power Fx), or should I move the logic to Power Automate?
Any working formula examples for detecting overlaps in SharePoint list records would be greatly appreciated.
Thanks!

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WarrenBelz 155,840 Most Valuable Professional on at

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Hi @MK-09020908-0,

The best you can do (which will not catch absolutely "concurrent" writes) is to check the modifled date/time of the current record with that of the one of the Form the user has retreived. So put a Label in any Data Card on your Form (you can hide it) with
ThisItem.Modified

and do something like this

If( Lookup( SPListName, ID = SharePointIntegration.SelectedListItemID ).Modified <> DateTimeValue(YourLabelName.Text), Notify( "This reservation has been updated since you selected it. Please re-select to see changes", NotificationType.Error, 5000 ), SubmitForm(FormName) )

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WarrenBelz 155,840 Most Valuable Professional on at

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Hi @MK-09020908-0,

A quick follow-up to see if you received the answer you were looking for. Happy to assist further if not.

Please ✅ Does this answer your question if my post helped you solve your issue. This will help others find it more readily. It also closes the item. If the content was useful in other ways, please consider answering Yes to Was this reply helpful? or give it a Like ♥
Visit my blog Practical Power Apps LinkedIn

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