class employee
...

 def product_ids_=(ids)
  return if id.to_s == ''
  Assignment.delete_all("assignment_type = 'EmployeeProduct' and employee_id = #{id}")
  ids.each do |i|
   self.assignments << EmployeeProduct.new(:entity_id => i, :employee_id => self.id) if i.to_s != ''
  end
 end

...
end