how to show the error message "The room was already booked" . i want to check by ** room_id,** start** , how it is possible?
py file
_columns = {
'room_id' : fields.many2one('room.management', string="Room Booking"),
'duration': fields.integer('Duration'),
'reason': fields.char('Reason',requierd=True ,help="short deatails about booking"),
'start': fields.datetime('Start At',requierd=True),
'end': fields.datetime('End At',requierd=True),
}