哪些错误与此LINQ查询

Question

var item1 = (from a in db.Item 
         where 
         (a.ItemNo == Item.ItemNo || Item.ItemNo==null) && 
         (a.StatusId == Item.StatusId || Item.StatusId == 0) && 
          (a.LocationId == Item.LocationId || Item.LocationId == 0) 
         select a).ToList(); 

      return View(item1); 

我得到异常

[ Argument # = 1,Name of function(if known) = isnull ] 

我也试过这个代码

var item1 = (from a in db.Item 
         where 
         (a.ItemNo == Item.ItemNo || Item.ItemNo=="") && 
         (a.StatusId == Item.StatusId || Item.StatusId == 0) && 
          (a.LocationId == Item.LocationId || Item.LocationId == 0) 
         select a).ToList(); 

      return View(item1); 

但不工作得到错误

[String truncation: max=0, len=2, value='10'. ] 

Answer 1

你可以尝试写它作为一个Lamdba的表情，看它是否是同样的问题？

var item1 = db.Item.Where(a => (String.IsNullOrEmpty(Item.ItemNo) || a.ItemNo == Item.ItemNo) && 
           (Item.StatusId == 0 || a.StatusId == Item.StatusId) && 
           (Item.LocationId == 0 || a.LocationId == Item.LocationId)).FirstOrDefault(); 

return View(item1); 

更新

出现EF不支持String.IsNullOrEmpty看到this question。您可以重新编写您的查询，如：

var item1 = db.Item.Where(a => ((Item.ItemNo == null || Item.ItemNo == String.Empty) || a.ItemNo == Item.ItemNo) && 
           (Item.StatusId == 0 || a.StatusId == Item.StatusId) && 
           (Item.LocationId == 0 || a.LocationId == Item.LocationId)) 
        .FirstOrDefault(); 

如果您仍然无法检查null，则可以将查询分解为例如

var query = db.Item.Where(a => (Item.StatusId == 0 || a.StatusId == Item.StatusId) && 
           (Item.LocationId == 0 || a.LocationId == Item.LocationId)); 

if (!String.IsNullOrEmpty(Item.ItemNo)) 
{ 
    query = query.Where(a => a.ItemNo == Item.ItemNo); 
} 

var item1 = query.FirstOrDefault(); 

Answer 2

编辑 尝试这样

string.IsNullOrEmpty(Item.ItemNo) ? a.ItemNo==a.ItemNo 
        : a.ItemNo == Item.ItemNo; 

代码soemthing对你来说是

var item1 = (from a in db.Item 
        where 
        (string.IsNullOrEmpty(Item.ItemNo) ? a.ItemNo==a.ItemNo 
        : a.ItemNo == Item.ItemNo;) && 
        ..more 

注意如果Item.ItemNo值为null或空比你应该做a.ItemNo==a.ItemNo SOT帽子它满足你的条件...

---

请确保您的itmeno字段为空，如下所示

int? ItemNo { get; set; } 

和试用soemthing这样

Item.ItemNo == null ? a.ItemNo : a.ItemNo == Item.ItemNo 

所以它已经

var item1 = (from a in db.Item 
        where 
        (Item.ItemNo == null ? a.ItemNo : a.ItemNo == Item.ItemNo) && 
        ..more