Question

我在一个更大的项目中拥有一个实用程序功能，该功能可以更新后端SQL数据库。我大多数时候都无法使用它，并显示以下错误：

已经有一个与此命令关联的打开的DataReader，必须先关闭它。

该功能的代码如下：

Public Function Update_Data(what As String, Optional where As String = "",
                            Optional table As String = ThisAddIn.defaultTable) As Integer
    Try
        Dim cmd As New SqlCommand With {
            .Connection = conn
        }

        cmd.CommandText = "UPDATE " & table & " SET " & what

        If where <> "" Then
            cmd.CommandText &= " WHERE " & where
        End If

        Update_Data = cmd.ExecuteNonQuery
        cmd.Dispose()
    Catch ex As Exception
        Update_Data = 0
        Debug.WriteLine("SQL Error updating data:" & vbCrLf & ex.Message)
    End Try
End Function

我已经遍历了代码的其余部分，以确保每当我声明一个SQLDataReader时，我以后都会调用reader.close()。我在其中添加了cmd.Dispose()行以及我可以找到的所有其他ExecuteNonQuery函数-万一有帮助？

还有其他可能未关闭的阅读器实例/类型吗？

Answer 1

在发生异常的情况下，您不会处置命令。

如果您不想使用Using，请添加一个Finally

 Public Function Update_Data(what As String, Optional where As String = "",
                             Optional table As String = ThisAddIn.defaultTable) As Integer
    Dim cmd As SqlCommand
    Try
        cmd = New SqlCommand With {.Connection = conn}
        cmd.CommandText = "UPDATE " & table & " SET " & what
        If where <> "" Then
            cmd.CommandText &= " WHERE " & where
        End If
        Update_Data = cmd.ExecuteNonQuery
    Catch ex As Exception
        Update_Data = 0
        Debug.WriteLine("SQL Error updating data:" & vbCrLf & ex.Message)
    Finally
        cmd.Dispose()
    End Try
End Function

但是Using可能更简单

 Public Function Update_Data(what As String, Optional where As String = "",
                             Optional table As String = ThisAddIn.defaultTable) As Integer
    Using cmd As New SqlCommand With {.Connection = conn}
        Try
            cmd.CommandText = "UPDATE " & table & " SET " & what
            If where <> "" Then
                cmd.CommandText &= " WHERE " & where
            End If
            Update_Data = cmd.ExecuteNonQuery
        Catch ex As Exception
            Update_Data = 0
            Debug.WriteLine("SQL Error updating data:" & vbCrLf & ex.Message)
        End Try
    End Using
End Function

我如何追踪未封闭的阅读器

1 个答案: