Question

我很难理解为什么我的记录数量与查询语句不同。现在作为一个新用户，我显然没有正确编码，但看不到它。如果我在访问中运行我的查询它返回正确数量的记录，但在vb.Net中，它返回一个完全不同的数字。

例如，在我的代码中

Sub filllistview()
    Try
        'creatconn()
        oledbCnn.ConnectionString = My.Settings.storageConnectionString
        oledbCnn.Open()
        'Dim oledbCmd As OleDbCommand = New OleDbCommand("Select TOP 100 * from Postings WHERE Customer = '" & newvar & "' ORDER BY Date DESC", oledbCnn)
        'dr = oledbCmd.ExecuteReader()

        'drcount = Convert.ToInt32(dr("RowCount"))
        Dim oledbCmd As OleDbCommand = New OleDbCommand("Select TOP 100 * from Postings " & _
                           "WHERE Customer = ? ORDER BY Date DESC", oledbCnn)
        oledbCmd.Parameters.AddWithValue("@p1", newvar)
        Using dr = oledbCmd.ExecuteReader()


            'clear items in the list before populating with new values
            ListView1.Items.Clear()

            While dr.Read()

                ListView1.Items.Add(CDate(dr(4)).ToShortDateString()).UseItemStyleForSubItems = False
                ListView1.Items(ListView1.Items.Count - 1).SubItems.Add(dr(1).ToString())
                ListView1.Items(ListView1.Items.Count - 1).SubItems.Add(dr(11).ToString())
                ListView1.Items(ListView1.Items.Count - 1).SubItems.Add(dr(7).ToString())
                With ListView1.Items(ListView1.Items.Count - 1).SubItems.Add(CDbl(dr(5)).ToString("C"))
                    If CDbl(dr(5)) < 0 Then
                        .ForeColor = Color.Red
                        .BackColor = Color.Gainsboro
                        '.Font = New Font(Font.FontFamily, Font.Size, FontStyle.Bold)
                    Else
                        .ForeColor = tmpColor
                    End If
                End With
                ListView1.Items(ListView1.Items.Count - 1).SubItems.Add(dr(14).ToString())
                ListView1.Items(ListView1.Items.Count - 1).SubItems.Add(dr(3).ToString())
                count += 1

            End While
        End Using
        MessageBox.Show(CStr(ListView1.Items.Count - 1))
        MessageBox.Show(count.ToString)

        'If (count < 100) Then
        '    MessageBox.Show("less than 100")

        'Else
        '    MessageBox.Show(count.ToString)
        'End If

        'autosize each column in listview
        For Each col As ColumnHeader In ListView1.Columns
            col.Width = -2
        Next col

        'refresh the list with new data
        ListView1.Refresh()

        'Enable the posting previous button
        'btnNextPostings.Enabled = True

    Catch ex As Exception
        MessageBox.Show(ex.Message)
    Finally
        'dr.Close()
        oledbCnn.Close()
    End Try

    'btnNextPostings.Enabled = ListView1.Items.Count > 100

    gbxPostings.Text = "Client Postings for: " & "( " & newvar & " )" & " Total Records: " & count

    If (ListView1.Items.Count < 100) Then
        btnNextPostings.Enabled = False
        btnNextPostings.Text = "No data to show"
    Else
        btnNextPostings.Enabled = True
        btnNextPostings.Text = "Next " & CStr(ListView1.Items.Count - 1) & " Postings"
    End If

End Sub

我哪里出错了。非常感谢

Answer 1

您似乎忘记在命令上调用ExecuteReader，因此，如果读取器实例已由先前的命令初始化，则您正在循环先前加载的内容。

Dim oledbCmd As OleDbCommand = New OleDbCommand("Select TOP 100 * from Postings " & _
                               "WHERE Customer = ? ORDER BY [Date] DESC", oledbCnn)
oledbCmd.Parameters.AddWithValue("@p1", newvar)
Using OleDbDataReader dr = oledbCmd.ExecuteReader()
   While dr.Read()
      ....
   End While
End Using

我还将命令文本从字符串连接更改为参数化查询。使用参数化查询来避免sql注入和解析问题非常重要。另一个变化是围绕一次性对象Using Statement（最重要的是连接，但在代码中不清楚如何初始化它）。最后，当您连接到Access数据库时，DATE这个词是OleDbProvider使用的Acces Jet Engine的保留关键字。你需要在这个词周围加上方括号。

当然，如果你想要精确计算ListView中的项目，你应该在开始阅读循环之前通过调用ListView.Items.Clear()删除（清除）以前的内容，并确保必须{{} 1}}全局变量正确初始化为零。

记录计数因查询而异

1 个答案: