OleDb 数据读取器问题

Question

我有一个使用 MySQL 数据库的 vb.net 程序。现在我将数据库更改为Microsoft Access 2010。我更改了所有必要的设置，如连接首选项、命令等。

问题是：我有一个错误

mydata = mycommand.ExecuteReader

它会产生错误：

错误 1 ​​类型“System.Data.OleDb.OleDbDataReader”的值无法转换为“MySql.Data.MySqlClient.OleDb.OleDbDataReader”

整个代码是：

 Public Sub showAlarm()
        Try
            Dim conn As New OleDb.OleDbConnection(connection)
            Dim myadapter As New OleDb.OleDbDataAdapter
            conn.Open()
            Dim sqlquery = "select * from alarm"
            Dim mycommand As New OleDb.OleDbCommand
            mycommand.Connection = conn
            mycommand.CommandText = sqlquery
            myadapter.SelectCommand = mycommand
            Dim mydata As MySqlDataReader
            mydata = mycommand.ExecuteReader
            'If mydata.HasRows = 0 Then
            '    MsgBox("Data Not Found")
            '    TextBox1.Clear()
            'Else
            mydata.Read()
            TextBox1.Text = mydata.Item("subhi")
            TextBox2.Text = mydata.Item("zuhur")
            TextBox3.Text = mydata.Item("aser")
            TextBox4.Text = mydata.Item("megrib")
            TextBox5.Text = mydata.Item("isha")
            'End If
            conn.Close()
        Catch ex As Exception
            MessageBox.Show("There is a problem with your connection!")
        End Try

    End Sub

如何解决这个问题？

Answer 1

由于 mycommand 是 OleDbCommand mycommand.ExecuteReader 返回 OleDbDataReader 但 mydata 是 MySqlDataReader。所以将mydata 更改为OleDbDataReader。

Dim mydata As OleDbDataReader = mycommand.ExecuteReader()

旁注：你应该使用Using-statement 来确保所有非托管资源都被释放：

Using conn As New OleDb.OleDbConnection(connection)
    Using mycommand As New OleDb.OleDbCommand("select * from alarm", conn)
        conn.Open()
        Using mydata = mycommand.ExecuteReader()
            If mydata.Read Then
                ' ... '
            End If
        End Using
    End Using
End Using