Question

如果找不到匹配项，我想检查下面的代码，它不应该抛出对象引用null错误。

 itm.lstCustomziation.AddRange(
     (from xx in db.vw_DressingCustomization
      where xx.CatID == itm.HeaderName.Value && xx.ProductID == itm.ProductID
      select new itmCustomization()
      {
          catId = (int)xx.CatID,
          custType = customizationType.Dressing,
          isCustomziationDisplay = xx.IsDefaultDisplay,
          isFixLimit = (bool)xx.isDefaultLimit,
          maxLimit = (short)xx.DefaultFreeCount,
          itmName = xx.Description,
          isItemDefault = xx.IsDefaultDisplay,
          price = (double)xx.MainPrice,
          proId = (int)xx.ProductID
      }).ToList<itmCustomization>());

Answer 1

你应该把它分成多个步骤。首先执行查询并获取结果。然后你应该检查null / count并根据该检查调用add range方法。它也会更具可读性。

Answer 2

在访问该值之前，请检查您的可空itm.HeaderName是否确实有值：

 where itm.HeaderName.HasValue &&  // check if value exists
       xx.CatID == itm.HeaderName.Value && // otherwise here is the problem
       xx.ProductID == itm.ProductID

有没有办法在AddRange（）方法中检查null对象的linq语句？

2 个答案: