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Additionally, there are functions available for performing calculations and filtering lists. When linked to a dimension, you can access special variables like overlapping_reservations overlappingReservations and matchingAvailabilities to further rules for availability checking or double bookings.

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When you link your rule to a dimension, two special variables will become available for use in the formula.

• overlapping_reservationsoverlappingReservations
  overlapping reservations with the reservation being checked
  COUNT(overlappingReservations) > 0
  This rule would make sure that no overlapping reservation are allowed

• matchingAvailablilities
  Allowing you to use the availability or unavailability of the related dimension in your formula.
  COUNT(matchingAvailabilities) == 0
  Reservation not allowed when there is no availability or if there are unavailabilities.

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You can also reference and check the permissions of the running user in your rule.
By adding: $Permission.Custom_Permission_Name
COUNT(overlapping_reservationsoverlappingReservations) > 0 and $Permission.B25__ALLOW_DOUBLE_BOOKING == false

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Reservation not allowed when overlapping with other reservation.

COUNT(overlapping_reservationsoverlappingReservations) > 0

Reservation not allowed if no availability

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• Reservation not allowed when overlapping with other reservations, not taking into account reservation with status “Canceled” AND status “Temporary”

COUNT(FILTER(overlapping_reservations overlappingReservations AS item, item.b25__status__r.name != ‘Canceled’ AND item.b25__status__r.name!="Temporary")) > 0

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Resource__r.Allow_Double_Booking__c == false AND COUNT(overlapping_reservationsoverlappingReservations) > 0

• Reservation not allowed when when overlapping with more reservations then specified at the “max capacity field specified on the related resource.

COUNT(overlapping_reservationsoverlappingReservations) > Resource__r.Max_Reservations__c

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• Reservations are not allowed to be double booked and when the running user doesn’t have the permission to “overrule double bookings”

COUNT(overlapping_reservationsoverlappingReservations) > 0 and $Permission.B25__ALLOW_DOUBLE_BOOKING == false

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