如何使用MYSQL在C＃中的datagridview中插入，刪除，選擇，更新值

Question

下面是使用datagridview將值插入mysql數據庫的代碼。 但是selectcommand是有效的。它不會發生，因為我收到錯誤消息，指出“列'username'不能為null”。

如果我使用ms Access數據庫，則不會彈出此錯誤。 誰可以幫我這個事。 還有其他方法可以這樣做。

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private void button1_Click(object sender, EventArgs e)
    {    //Even using functions we can easily update the datagridview
        //Select_function();

        try
        {   //The container which displays the details.
            dataGridView1.Visible = true;

            //The binding object which binds the datagridview with backend.
            BindingSource bs = new BindingSource();

            //The datatable through which data is exported to datagridview
            table = new DataTable();
            bs.DataSource = table;
            this.dataGridView1.DataSource = bs;

            MySqlConnection conn = new MySqlConnection(db);
            conn.Open();

            string s = "select *from user";
            cmd = new MySqlCommand(s, conn);

            da = new MySqlDataAdapter();
            da.SelectCommand = new MySqlCommand(s, conn);

            //There is issue in below sytax of insert command.
            MySqlCommand insertcommand = new MySqlCommand("insert into user(username,password) values(@username ,@password)", conn);
            insertcommand.Parameters.Add("username",MySqlDbType.VarChar,50,"username");
            insertcommand.Parameters.Add("password", MySqlDbType.VarChar, 50, "password");
            da.InsertCommand = insertcommand;


            //Demonstrates update command
            MySqlCommand updatecommand = new MySqlCommand("update user set username=@username,password=@password where (username=@username)", conn);
            updatecommand.Parameters.Add("@username", MySqlDbType.VarChar, 50, "username");
            updatecommand.Parameters.Add("@password", MySqlDbType.VarChar, 50, "password");

             da.UpdateCommand = updatecommand;



            //Demonstration of delete Command
            MySqlCommand deletecommand = new MySqlCommand("delete from user where username=@username", conn);
            deletecommand.Parameters.Add("@username", MySqlDbType.VarChar, 50, "username");
            da.DeleteCommand = deletecommand;

            da.Fill(table);
            conn.Close();

        }
        catch (Exception err) { MessageBox.Show(err.Message); } 

    }
    private void button2_Click(object sender, EventArgs e)
    {  da.Update(table);
    }

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Answer 1

我不太確定，但是mysql是否不使用帶有“？”-synatx的編號參數或帶有“：”-syntax而不是（mssql）at-syntax的命名參數？

就像是 ：

MySqlCommand insertcommand = new MySqlCommand("insert into user(username,password) values(?, ?)", conn);
insertcommand.Parameters.Add(1, MySqlDbType.VarChar,50,"username");
insertcommand.Parameters.Add(2, MySqlDbType.VarChar, 50, "password");

要么

MySqlCommand insertcommand = new MySqlCommand("insert into user(username,password) values(:username, :pass)", conn);
insertcommand.Parameters.Add(":username", MySqlDbType.VarChar,50,"username");
insertcommand.Parameters.Add(":pass", MySqlDbType.VarChar, 50, "password");

Answer 2

我認為您需要更改添加到insert命令的參數的名稱，以匹配INSERT SQL語句中指定的名稱。

嘗試：

insertcommand.Parameters.Add("@username",MySqlDbType.VarChar,50,"username");
insertcommand.Parameters.Add("@password", MySqlDbType.VarChar, 50, "password");

Answer 3

在使用datagrid（vb.net）在mysql中更新時遇到了類似的問題。 解決了：

Dim cmb As New MySqlCommandBuilder(datGrid)
Me.datGrid.Update(datSet, "mysqlTableToUpdate")