sample.py

class DepartmentAdmin(admin.ModelAdmin):
    
    def formfield_for_foreignkey(self, db_field, request, **kwargs):
        if db_field.name == "employee":
          ''' The idea here is to read the string in request path as when django edits a field it has its key at the end of the string after add'''
            request_path_array = filter(None,request.path.split('/'))
            if request_path_array[len(request_path_array)-1] !="add":
              '''Now get all the employee with particular department id'''
                kwargs["queryset"] = Employee.objects.filter(departmentid=request_path_array[len(request_path_array)-1])
                return db_field.formfield(**kwargs)
        return super(DepartmentAdmin, self).formfield_for_foreignkey(db_field, request, **kwargs)