LINQ to Dataset DBNULL 问题/空引用异常

发布于 2024-07-21 03:40:15 字数 1418 浏览 4 评论 0原文

我有以下 LINQ 查询，当 dtblDetail 中的“Remark”列为 null 时，它总是会导致错误，即使我测试它是否为 NULL。

var varActiveAndUsedElementsWithDetails =
                        from e in dtblElements
                        join d in dtblDetails on e.PK equals d.FK into set
                        from d in set.DefaultIfEmpty()
                        where (e.ElementActive == true)
                        select new
                        {
                            ElementPK = e.PK,
                            Remark = d.IsRemarkNull() ? null : d.Remark
                        };

错误消息是： “表‘dtblDetails’中‘备注’列的值为 DBNull。” 添加 d.IsRemarkNull() 测试后，会引发空引用异常。

你能帮我解决这个问题吗？

我已经检查了以下网站，但除了我必须测试 DBNULL 之外没有发现任何有用的东西。但正如我所说，这并不能解决我的问题。

原文

I have the following LINQ query which always results in an error when my "Remark" column in dtblDetail is null, even though I test if it is NULL.

var varActiveAndUsedElementsWithDetails =
                        from e in dtblElements
                        join d in dtblDetails on e.PK equals d.FK into set
                        from d in set.DefaultIfEmpty()
                        where (e.ElementActive == true)
                        select new
                        {
                            ElementPK = e.PK,
                            Remark = d.IsRemarkNull() ? null : d.Remark
                        };

The error message was:
"The value for column 'Remark' in table 'dtblDetails' is DBNull."
After adding the test for d.IsRemarkNull() a null reference exception is thrown.

Can you help me with this?

I've already checked the following websites but didn't find anything useful other than that I have to test for DBNULL. But as said this doesn't solve my problem.

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太阳男子 2024-07-28 03:40:15

问题是整个“d”项是空的。
因此调用“d.IsRemarkNull()”会导致空引用异常。
以下代码解决了该问题：

var varActiveAndUsedElementsWithDetails =
                    from e in dtblElements
                    join d in dtblDetails on e.PK equals d.FK into set
                    from d in set.DefaultIfEmpty()
                    where (e.ElementActive == true)
                    select new
                    {
                        ElementPK = e.PK,
                        Remark = d == null? null : (d.IsRemarkNull() ? null : d.Remark)
                    };

The problem was that the whole 'd' item was empty.
So calling 'd.IsRemarkNull()' resulted in the null reference exception.
The following code fixed the problem:

var varActiveAndUsedElementsWithDetails =
                    from e in dtblElements
                    join d in dtblDetails on e.PK equals d.FK into set
                    from d in set.DefaultIfEmpty()
                    where (e.ElementActive == true)
                    select new
                    {
                        ElementPK = e.PK,
                        Remark = d == null? null : (d.IsRemarkNull() ? null : d.Remark)
                    };

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