位置 0 Vb.net 和 Mysql 没有行

Question

我试图从表“打印机”上的“状态”行获取和打印数据，但它一直说“位置 0 没有行”。

 Dim conn As New deepconnection()
    Dim adapter As New MySqlDataAdapter()
    Dim table As New DataTable()
    Dim ds, ds1 As New DataSet
    Dim command As New MySqlCommand("SELECT * FROM printer", conn.getConnection)
    conn.openOcean()
    PrinterStatus.Text = table.Rows(0).Item("status")

连接：

 Private fishcatch As New MySqlConnection("datasource=localhost;port=3306;username=root;password=xxxxx;database=deep_ocean")

' Get the connection only to read
ReadOnly Property getConnection() As MySqlConnection
    Get
        Return fishcatch
    End Get
End Property

打开连接：

Sub openOcean()
    If fishcatch.State = ConnectionState.Closed Then
        fishcatch.Open()
    End If
End Sub

怎么了？

Answer 1

您尚未执行填充表的命令。 没有那部分，桌子仍然是空的

Dim command As New MySqlCommand("SELECT * FROM printer", conn.getConnection)
conn.openOcean()

' Execute the command and pass the reader to the table load method
table.Load(command.ExecuteReader())

PrinterStatus.Text = table.Rows(0).Item("status")

即使在此之后，如果名为 Printer 的数据库表中没有记录，该表仍可能为空，因此在从数据表中读取任何内容之前，请始终检查行数

If table.Rows.Count > 0 Then
    PrinterStatus.Text = table.Rows(0).Item("status")
    ...
End If