C# linq-to-sql datacontext nullreferenceexception

LINQ to SQL DataContext 中的空引用异常

发布于 2024-08-03 07:38:35 字数 1317 浏览 6 评论 0原文

我有一个由这段代码引起的空引用异常：

var recentOrderers = (from p in db.CMS
            where p.ODR_DATE > DateTime.Today - new TimeSpan(60, 0, 0, 0)
            select p.SOLDNUM).Distinct();
result = (from p in db.CMS
             where p.ORDER_ST2 == "SH" &&
                   p.ODR_DATE > DateTime.Today - new TimeSpan(365, 0, 0, 0) &&
                   p.ODR_DATE < DateTime.Today - new TimeSpan(60, 0, 0, 0) &&
                   !(recentOrderers.Contains(p.SOLDNUM))/**/
             select p.SOLDNUM).Distinct().Count();

结果是双精度类型。当我注释掉时：

!(recentOrderers.Contains(p.SOLDNUM))

代码运行良好。我已经验证了recentOrderers不为空，并且当我运行：

if(recentOrderes.Contains(0)) return;

执行时遵循此路径并返回。不知道发生了什么，因为我在上面使用了类似的代码：

var m = (from p in db.CMS where p.ORDER_ST2 == "SH" select p.SOLDNUM).Distinct();
            double result = (from p in db.CUST
                        join r in db.DEMGRAPH on p.CUSTNUM equals r.CUSTNUM
                        where p.CTYPE3 == "cmh" && !(m.Contains(p.CUSTNUM)) &&
                              r.ColNEWMEMBERDAT.Value.Year > 1900
                        select p.CUSTNUM).Distinct().Count();

它也运行完美。注意到相似之处后，有人可以帮忙吗？提前致谢。

原文

I have a Null Reference Exception Caused by this code:

var recentOrderers = (from p in db.CMS
            where p.ODR_DATE > DateTime.Today - new TimeSpan(60, 0, 0, 0)
            select p.SOLDNUM).Distinct();
result = (from p in db.CMS
             where p.ORDER_ST2 == "SH" &&
                   p.ODR_DATE > DateTime.Today - new TimeSpan(365, 0, 0, 0) &&
                   p.ODR_DATE < DateTime.Today - new TimeSpan(60, 0, 0, 0) &&
                   !(recentOrderers.Contains(p.SOLDNUM))/**/
             select p.SOLDNUM).Distinct().Count();

result is of double type. When I comment out:

!(recentOrderers.Contains(p.SOLDNUM))

The code runs fine. I have verified that recentOrderers is not null, and when I run:

if(recentOrderes.Contains(0)) return;

Execution follows this path and returns. Not sure what is going on, since I use similar code above it:

var m = (from p in db.CMS where p.ORDER_ST2 == "SH" select p.SOLDNUM).Distinct();
            double result = (from p in db.CUST
                        join r in db.DEMGRAPH on p.CUSTNUM equals r.CUSTNUM
                        where p.CTYPE3 == "cmh" && !(m.Contains(p.CUSTNUM)) &&
                              r.ColNEWMEMBERDAT.Value.Year > 1900
                        select p.CUSTNUM).Distinct().Count();

which also runs flawlessly. After noting the similarity, can anyone help? Thanks in advance.

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椵侞 2024-08-10 07:38:35

我对 Linq 不太熟悉，但是如果没有匹配结果，.Distinct() 是否会返回 null？

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柠栀 2024-08-10 07:38:35

尝试通过转换为列表对象（实际上：使用 .ToList() 执行它）来显式从第一个查询获取数据，然后进行比较。

var recentOrderers = (from p in db.CMS
            where p.ODR_DATE > DateTime.Today - new TimeSpan(60, 0, 0, 0)
            select p.SOLDNUM).Distinct().ToList();

Try to explicite get data from the first query by converting to a list object (actually: executing it using .ToList()) then use in comparison.

var recentOrderers = (from p in db.CMS
            where p.ODR_DATE > DateTime.Today - new TimeSpan(60, 0, 0, 0)
            select p.SOLDNUM).Distinct().ToList();

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