序列包含多个元素

Question

我在通过Linq获取"RhsTruck"类型列表并让它们显示时遇到了一些问题.

RhsTruck只有Make,Model,Serial等... RhsCustomer有属性CustomerName,CustomerAddress等...

我一直收到错误"序列包含多个元素".有任何想法吗？我是以错误的方式接近这个吗？

public RhsCustomer GetCustomer(string customerNumber)
{
    using (RhsEbsDataContext context = new RhsEbsDataContext() )
    {
        RhsCustomer rc = (from x in context.custmasts
                          where x.kcustnum == customerNumber
                          select new RhsCustomer()
                        {
                            CustomerName = x.custname,
                            CustomerAddress = x.custadd + ", " + x.custcity
                            CustomerPhone = x.custphone,
                            CustomerFax = x.custfax
                        }).SingleOrDefault();
        return rc;
    }
}

public List<RhsTruck> GetEquipmentOwned(RhsCustomer cust)
{
    using (RhsEbsDataContext context = new RhsEbsDataContext())
    {
        var trucks = (from m in context.mkpops
                      join c in context.custmasts
                        on m.kcustnum equals c.kcustnum
                      where m.kcustnum == cust.CustomerNumber
                      select new RhsTruck
                    {
                        Make = m.kmfg,
                        Model = m.kmodel,
                        Serial = m.kserialnum,
                        EquipID = m.kserialno1,
                        IsRental = false
                    }).ToList();
        return trucks;
    }
}

protected void Page_Load(object sender, EventArgs e)
{
    string testCustNum = Page.Request.QueryString["custnum"].ToString();

    RhsCustomerRepository rcrep = new RhsCustomerRepository();
    RhsCustomer rc = rcrep.GetCustomer(testCustNum);
    List<RhsTruck> trucks = rcrep.GetEquipmentOwned(rc);

    // I want to display the List into a Gridview w/auto-generated columns
    GridViewTrucks.DataSource = trucks;
    GridViewTrucks.DataBind();   
}

Answer 1

问题是你正在使用SingleOrDefault.只有当集合包含0或1个元素时,此方法才会成功.FirstOrDefault无论集合中有多少元素,我相信您正在寻找哪种成功.

Answer 2

SingleOrDefaultException如果序列中有多个元素,则抛出一个方法.

显然,您的查询GetCustomer是找到多个匹配项.因此,您需要优化查询,或者最有可能检查您的数据,以了解您为什么获得给定客户编号的多个结果.

Answer 3

Use FirstOrDefault insted of SingleOrDefault..

SingleOrDefault 返回一个 SINGLE 元素，如果没有找到元素，则返回 null。如果在您的 Enumerable 中找到 2 个元素，则它会抛出您看到的异常

FirstOrDefault 返回它找到的第一个元素，如果没有找到元素，则返回 null。因此，如果有 2 个元素与您的谓词匹配，则忽略第二个元素

   public int GetPackage(int id,int emp)
           {
             int getpackages=Convert.ToInt32(EmployerSubscriptionPackage.GetAllData().Where(x
   => x.SubscriptionPackageID ==`enter code here` id && x.EmployerID==emp ).FirstOrDefault().ID);
               return getpackages;
           }

 1. var EmployerId = Convert.ToInt32(Session["EmployerId"]);
               var getpackage = GetPackage(employerSubscription.ID, EmployerId);