我希望 datareader 从数据库中的 varchar 列读取数据，并将读取结果存储在字符串变量中

Question

我希望 datareader 从数据库中的 varchar 列读取数据，并将读取结果存储在字符串变量中，但它会生成一个 indexoutofrange 异常...基本上我想要一个验证，以便如果用户输入已经是的预订时间在数据库中，程序应该生成一条错误消息。如果输入的值在预订的持续时间内，也会生成错误。例如，如果预订于 2011 年 12 月 12 日下午 4:00 进行且持续时间为 2 小时，则该程序不应允许在下午 6:00 之前进行任何预订，除非预订是针对某些其他游戏或某些其他球场（如果是羽毛球、壁球、草地网球等）

我正在尝试以下代码：

Dim str2 As String ' 定义用于进行选择查询的字符串变量

    str2 = "select booking_date, booking_time, booking_duration, poolno, courtno, tableno from Bookings"

    Dim a, b As Date
    Dim c As Date
    Dim d, f, g, l As String

    Dim dur As Integer

    Dim cmd2 As New SqlCommand(str2, con)
    con.Open()

    Dim bookchk As SqlDataReader = cmd2.ExecuteReader
    While bookchk.Read()
        a = bookchk("booking_date")
        b = bookchk("booking_time")
        c = b.ToLongTimeString
        dur = bookchk("booking_duration")

        l = bookchk("game") 'exception is generated here


        If CmboGame.SelectedItem = "Swimming" Then
            If bookchk("poolno") IsNot System.DBNull.Value Then
                d = bookchk("poolno")

            End If

        Else : d = ""

        End If

        If CmboGame.SelectedItem = "Table Tennis" Then
            If bookchk("tableno") IsNot System.DBNull.Value Then
                f = bookchk("tableno")

            End If
        Else : f = ""
        End If
        If CmboGame.SelectedItem IsNot "Table Tennis" And CmboGame.SelectedItem IsNot "Swimming" Then
            If bookchk("courtno") IsNot System.DBNull.Value Then
                g = bookchk("courtno")

            End If
        Else : g = ""
        End If
        If TxtBookDate.Text = a And TxtBookTime.Text = c And TxtPoolNo.Text = d And TxtCrtNo.Text = g And TxtTblNo.Text = f And CmboGame.SelectedItem = l Then
            MessageBox.Show("The date and time you have entered has already been booked" & vbCrLf & "Try Again!", "Bookings Overlapped", MessageBoxButtons.OK, MessageBoxIcon.Stop)
            Exit Sub

        End If


        Dim time, h, i, j, n As DateTime
        n = c.AddHours(dur)
        time = TxtBookTime.Text
        h = time.AddHours(TxtBookDur.Text)
        i = time.ToLongTimeString
        j = h.ToLongTimeString


        If TxtBookDate.Text = a And TxtPoolNo.Text = d And TxtCrtNo.Text = g And TxtTblNo.Text = f And CmboGame.SelectedIndex = l And i > c And i <= n Or j > n Then
            MessageBox.Show("The date and time you have entered has already been booked" & vbCrLf & "Try Again!", "Bookings Overlapped", MessageBoxButtons.OK, MessageBoxIcon.Stop)

            Exit Sub

        End If


    End While
    bookchk.Close()
    con.Close()

Answer 1

您的 SQL 语句：

str2 = "select booking_date, booking_time, booking_duration, poolno, courtno, tableno from Bookings"

您没有选择名为“game”的列，因此显然您无法在数据读取器中引用它。在SQL语句中添加“game”列，假设它存在，这个问题就会消失。当然，您可能还有其他问题。