[Django]-Django form queryset multiple same field filter

Your current query is trying to find employees which have department id 18 and 19 and 20. If department is a foreign key, that is not possible.

You can use Q() objects to find employees which have department id 18 or 19 or 20.

Employee.objects.filter(Q(department=18)|Q(department=19)|Q(department=20))

However in your case, the simplest solution is to use __in to return employees where the department id is any one of 18, 19 or 20.

Employee.objects.filter(department__in=[18, 19, 20])