Deleting items makes empty Reservation

When an Item is reserved it generates a link in the Database between some tables.

If i delete the Item that got reserved the Item is gone but all the reservations are still existing and cant be deleted because it then shows "the Item is not available". So i need to delete the reservation entriey by hand from my DB.

Do i do something wrong in my delete Prozess ?

Its not realy possible for me to first revoke all reservations because there are to many users i would need to check and just deleting the items gets this wierd "bug".

All Help is welcome