在vb.net中连接到mysql

Question

我试图在Visual Basic 2010中从VB.NET连接MySql。我想查询数据库，只是想获得一个返回就是单击按钮后对proID的响应。 它成功显示连接已建立，但我似乎无法在其上运行任何sql查询。 可能是什么问题？

这是我从即时窗口中得到的错误：

A first chance exception of type 'System.InvalidOperationException' occurred in MySql.Data.dll

假设num是按键事件的1001。

Public Class Form1
    Private connStr As String = "server=localhost;" & _
                "user id=root;Password=1234561;" & _
                "database = test"
    Dim num As Integer


Private Sub TextBox1_keypress(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress
    Dim str As String
    If e.KeyChar = Microsoft.VisualBasic.ChrW(Keys.Enter) Then
        str = TextBox1.Text
        Dim splitVals As String() = str.Split(" ")
        num = splitVals(1)
    End If
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim query As String = "SELECT * FROM products"
    Dim con As New MySqlConnection(connStr)
    Dim cmd As New MySqlCommand(query)
    Try
        con.Open()
        MessageBox.Show("Database Connected")
        cmd.ExecuteNonQuery()
        cmd.Connection.Close()

        con.Close()
    Catch ex As Exception
        Console.WriteLine(ex.Message)
    End Try
End Sub

End Class

Answer 1

试试这个代码：

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim query As String = "SELECT * FROM products"
    Dim con As New MySqlConnection(connStr)
    Dim da as New MySqlDataAdapter() 
    Dim ds as New DataSet
    Try
        con.Open()
        MessageBox.Show("Database Connected")
        da=New MySqlDataAdapter(query,con)
        da.fill(ds,"products") 
        DataGridView1.DataSource=ds.Tables("products")
        con.Close()
    Catch ex As Exception
        Console.WriteLine(ex.Message)
    End Try
End Sub

Answer 2

ExecuteNonQuery用于不返回任何数据的SQL语句（例如INSERT，UPDATE，DELETE）。

您想实现什么？ 如果要从product表中获取所有记录并将其显示在datagrid ，请尝试以下操作：

Using xConn as New MySqlConnection(connStr)
    Using xComm as new MySQLCommand()
        xComm.Connection = xConn
        xComm.CommandText = "SELECT * FROM products"
        Using xAdapter as new MySQLDAtaAdapter(xComm)
            Dim ds as new Dataset
            xConn.Open()
            xAdapter.Fill(ds)
            datagridview1.datasource = ds.tables(0)
        End Using
    End Using
End Using

更新1

Dim xPrice as Integer = 0
Using xConn as New MySqlConnection(connStr)
    Using xComm as new MySQLCommand()
        xComm.Connection = xConn
        xComm.CommandText = "SELECT ProductPrice FROM products WHERE proID = @xID"
            xComm.Parameters.AddWithValue("xID", "Value Here")
            xConn.Open()
            xPrice = CInt(xComm.ExecuteScalar())
            xConn.Close
    End Using
End Using

Msgbox xPrice