c# - 必须声明标量变量 "@UserName"

Question

我不断收到我不理解的错误。

Must declare the scalar variable "@varname"

我的目标是创建一个使用 2 个文本框和一个按钮的登录页面，它根据存储在 SQL 数据库中的信息检查用户是否退出。

这就是我认为问题的来源:

private bool DBConnection(string userName, string password)
{
    SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);
    
    //string cmdString = ("SELECT UserName, Password FROM Users WHERE UserName ='" + userName +
    //                    "'AND Password ='" + password + "'");         //REMOVED AS THIS IS PRONE TO SQL INJECTIONS
    
    string cmdString = ("SELECT * FROM Users WHERE UserName = @uname AND Password = @pw");
    
    SqlCommand cmd = new SqlCommand(cmdString, conn);
    
    cmd.Parameters.Add("uname", SqlDbType.VarChar).Value = userName;
    cmd.Parameters.Add("pw", SqlDbType.VarChar).Value = password;

    DataSet loginCredentials = new DataSet();
    SqlDataAdapter dataAdapter;

    try
    {
        if (conn.State.Equals(ConnectionState.Closed))
        {
            conn.Open();

            dataAdapter = new SqlDataAdapter(cmdString, conn);
            dataAdapter.Fill(loginCredentials);

            conn.Close();

            if (loginCredentials != null)
            {
                if (loginCredentials.Tables[0].Rows.Count > 0)
                {
                    return true;
                }
                else
                {
                    lblMessage.Text = "Incorrect Username or Password";
                    lblMessage.Visible = true;
                }
            }   
        }
    }
    catch (Exception err)
    {
        lblMessage.Text = err.Message.ToString() + " Error connecting to the Database // " + cmd.Parameters.Count;
        lblMessage.Visible = true;
        return false;
    }

    return false;
}

特别是 dataAdapter.Fill(loginCredentials); 被执行的地方。

注释掉的语句在使用正确的用户名和密码登录用户时成功运行，但据我所知并不安全，因为它容易受到 SQL 注入(inject)的攻击，这就是我尝试参数化 SQL 的原因声明。

错误截图如下:

Answer 1

您应该将 sqlcommand 传递给 dataAdapter，因为在您的情况下，sqlcommand (cmd) 包含的信息不仅仅是命令文本和连接字符串。您的代码可能如下所示:

private bool DBConnection(string userName, string password)
{
 SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);

//string cmdString = ("SELECT UserName, Password FROM Users WHERE UserName ='" + userName +
//                    "'AND Password ='" + password + "'");         //REMOVED AS THIS IS PRONE TO SQL INJECTIONS

string cmdString = ("SELECT * FROM Users WHERE UserName = @uname AND Password = @pw");

SqlCommand cmd = new SqlCommand(cmdString, conn);

cmd.Parameters.Add("uname", SqlDbType.VarChar).Value = userName;
cmd.Parameters.Add("pw", SqlDbType.VarChar).Value = password;

DataSet loginCredentials = new DataSet();
SqlDataAdapter dataAdapter;

try
{
    if (conn.State.Equals(ConnectionState.Closed))
    {
        conn.Open();

        dataAdapter = new SqlDataAdapter(cmd);
        dataAdapter.Fill(loginCredentials);

        conn.Close();

        if (loginCredentials != null)
        {
            if (loginCredentials.Tables[0].Rows.Count > 0)
            {
                return true;
            }
            else
            {
                lblMessage.Text = "Incorrect Username or Password";
                lblMessage.Visible = true;
            }
        }   
    }
}
catch (Exception err)
{
    lblMessage.Text = err.Message.ToString() + " Error connecting to the Database // " + cmd.Parameters.Count;
    lblMessage.Visible = true;
    return false;
}

return false;
}