我在Web应用程序中具有ASMX service的以下代码。尝试获取XML格式的数据。为了清楚起见，我删除了一些数据

    /// <summary>
    /// Summary description for CompanyServices
    /// </summary>
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    [System.ComponentModel.ToolboxItem(false)]
    // To allow this Web Service to be called from script,using ASP.NET AJAX,uncomment the following line. 
    // [system.web.Script.Services.scriptservice]
    public class CompanyServices: system.web.Services.WebService
    {
        [WebMethod]
        public List<Product> GetData(int companyId,int custId)
        {
          return ProductService.getcompanyData(companyId,custId).ToList();
        }

在调试模式下所有运行，但我不断收到错误消息

System.InvalidOperationException: There was an error generating the XML document. ---> System.InvalidOperationException: A circular reference was detected while serializing an object of type Company

所以我创建了相同的类型，并且围绕它的每个循环都使用了类似的

foreach (Product p in ProductService.getcompanyData(companyId,custId).ToList())
{
  Product newProd = new Product
  newProd.Name = p.Name;
  newProd.Department = p.Department;
}

这一直有效，直到我添加了Department，该部门已链接到另一个表（部门）

在Google周围四处搜寻，但不知道是什么原因引起的或如何解决？