c# - 不会使用executeScalar()检查用户是否存在

Question

我想检查我的 MySQL 数据库中是否已存在用户。我确实在数据库中插入了一个用户，并想检查该用户是否存在。当用户在文本框中插入内容时，我希望它验证用户名。我也尝试过:OnTextChanged =“TextBoxUN_TextChanged”并将代码复制到TextBoxUN_TextChanged内。

这是到目前为止我的代码。

protected void Page_Load(object sender, EventArgs e)
    {
        if (IsPostBack) {
           string server = "wisteria.arvixe.com";
           string database = "greenhouse";
           string uid = "******";
           string password = "******";
            string connectionString;
            connectionString = "SERVER=" + server + ";" + "DATABASE=" +
            database + ";" + "UID=" + uid + ";" + "PASSWORD=" + password + ";";

            MySqlConnection connection = new MySqlConnection(connectionString);
            connection.Open();
            string cmd = "SELECT COUNT(*) FROM registration WHERE Username='" + TextBoxUN.Text + "'";
            MySqlCommand userExist = new  MySqlCommand(cmd, connection);
            int temp = Convert.ToInt32(userExist.ExecuteScalar().ToString());               
            connection.Close();
            if (temp == 1)
            {
                Response.Write("User already exist..!!!");
            }
        }

    }

希望大家能帮忙。抱歉我的英语不好

Answer 1

替换这一行:

int temp = Convert.ToInt32(userExist.ExecuteScalar().ToString());

用这一行:

int temp = (Int32)cmd.ExecuteScalar();