如何使用sqlreader从VB.NET中读取SQL数据 [英] How do I read data from SQL in VB.NET using sqlreader

问题描述

我尝试实现以下场景。

当用户点击按钮5时，它从数据库获取表号和时间，然后取决于button1，button2的时差变化颜色。

i还有包含tableno和time列的数据库。

以下代码给我具体演员无效错误。为什么？

谢谢任何帮助



我尝试过：

i try to achieve following scenario.
when user click button 5 its get table number and time from database then depend on time difference change color of button1,button2.
i also have database with tableno and time columns.
following code give me "specific cast is not valid" error.why?
thank you for any help

What I have tried:

Dim d1 As DateTime = DateTime.Parse(ToolStripStatusLabel1.Text)

Dim connString As String = "server=DESKTOP-69QA9LH\SQLEXPRESS; database=servicedb; integrated security=true"
Using conn As New SqlConnection(connString)
    conn.Open()

    Dim query As String
    query = "select time,tableno from restaurant "
    Using command = New SqlCommand(query, conn)
        Using reader = command.ExecuteReader
            While reader.Read()

                REM
                Dim time As DateTime = reader.GetDateTime(0)
                REM
                Dim tableNo As Int32 = reader.GetInt32(1)

                Dim diff As Long = DateDiff(DateInterval.Minute, time, d1)

                If tableNo = 2 AndAlso diff >= 5 Then
                    Button3.BackColor = Color.LawnGreen
                End If
                If tableNo = 2 AndAlso diff >= 10 Then
                    Button3.BackColor = Color.LawnGreen
                End If
                If tableNo = 2 AndAlso diff >= 15 Then
                    Button3.BackColor = Color.LawnGreen
                End If
                If tableNo = 1 AndAlso diff >= 5 Then
                    Button1.BackColor = Color.Brown
                End If
                If tableNo = 1 AndAlso diff >= 10 Then
                    Button1.BackColor = Color.Brown
                End If
                If tableNo = 1 AndAlso diff >= 15 Then
                    Button1.BackColor = Color.Brown
                End If
            End While
        End Using
    End Using
End Using

推荐答案

猜测 - 这就是全部，我们无法访问您的数据 - 有两个地方你可能会收到这个错误：

At a guess - and that's all it can be, we don't have access to your data - there are two places you might get this error:

Dim d1 As DateTime = DateTime.Parse(ToolStripStatusLabel1.Text)

如果用户输入错误的日期。

解决方案：使用 DateTime.TryParse [ ^ ]相反，并向用户报告问题。



或：

If the user enters a bad date.
Solution: use DateTime.TryParse[^] instead, and report problems to teh user.

Or:

Dim time As DateTime = reader.GetDateTime(0)
REM
Dim tableNo As Int32 = reader.GetInt32(1)

如果您的数据库不包含您认为应该包含的内容，或包含两列中的NULL值。

解决方案：检查数据库并确切了解其中的内容。 time 应该是DATETIME列，并且不包含空值。 tableno 应为INT且不包含空值。

If your DB does not contain what you think it should, or contains NULL values in either column.
Solution: Check your DB and see exactly what is there. time should be a DATETIME column, and contain no nulls. tableno should be an INT and contain no nulls.

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