LINQ 错误类型 DBNull 列

发布于 2024-11-04 06:36:13 字数 337 浏览 1 评论 0原文

我正在查询 datagridview，除非其中一个单元格没有任何内容（dbnull），否则它会很好地工作。如何克服这个？

例外：未为类型“DBNull”和类型“DBNull”定义运算符“=”。

Dim query = From row As DataGridViewRow In DataGridView1.Rows _
            Where row.Cells(SelectedColumnIndex).Value = filter _
            And row.Visible = False _
            Select row Distinct

原文

I am querying a datagridview and it works great unless one of the cells has nothing (dbnull). How to over come this?

Exceptions: Operator '=' is not defined for type 'DBNull' and type 'DBNull'.

Dim query = From row As DataGridViewRow In DataGridView1.Rows _
            Where row.Cells(SelectedColumnIndex).Value = filter _
            And row.Visible = False _
            Select row Distinct

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绅士风度i 2024-11-11 06:36:13

使用 .Equals() 方法比较可能为 null 的值。示例：

Dim query = From row As DataGridViewRow In DataGridView1.Rows _
        Where row.Cells(SelectedColumnIndex).Value.Equals(filter) _
        And !(row.Visible) _
        Select row Distinct

或者如果两者都可能为 null，则可以使用基本 Object.Equals() 方法进行比较：

Dim query = From row As DataGridViewRow In DataGridView1.Rows _
            Where Object.Equals(row.Cells(SelectedColumnIndex).Value, filter) _
            And !(row.Visible) _
            Select row Distinct

Use the .Equals() method to compare values in which one may be null. Example:

Dim query = From row As DataGridViewRow In DataGridView1.Rows _
        Where row.Cells(SelectedColumnIndex).Value.Equals(filter) _
        And !(row.Visible) _
        Select row Distinct

Or if both may be null, you can use the base Object.Equals() method to compare:

Dim query = From row As DataGridViewRow In DataGridView1.Rows _
            Where Object.Equals(row.Cells(SelectedColumnIndex).Value, filter) _
            And !(row.Visible) _
            Select row Distinct

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