LINQ错误类型为DBNull列

Question

我正在查询一个datagridview，它工作得很好，除非其中一个单元格没有任何东西(dbnull)。如何克服这一点?

异常:对于类型'DBNull'和'DBNull'没有定义运算符'='。

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

Answer 1

使用.Equals()方法比较可能为空的值。例子:

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

或者如果两者都为null，您可以使用基本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