用户注册-asp.net时，用户名检查不起作用

Question

我想检查用户名是否已存在于数据库中，如果是，错误消息将提示“用户名已存在”。 现在我有此代码，但无法正常工作。 即使从数据库复制了用户名，程序仍会接受该用户名。 有人可以帮我吗？ 这是我的完整注册码：

protected void Page_Load(object sender, EventArgs e)
    {
        if (IsPostBack)
        {
            SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["RegistrationConnectionString"].ConnectionString);
            conn.Open();
            string checkuser = "select count(*) from UserData where Username = '" + txtUser.Text + "'";
            SqlCommand scm = new SqlCommand(checkuser, conn);
            int temp = Convert.ToInt32(scm.ExecuteScalar().ToString());
            if (temp == 1) // check if user already exist.
            {
                Response.Write("User already existing");
            }
            conn.Close();
        }
    }
    protected void btn_Registration_Click(object sender, EventArgs e)
    {
        try
        {
            SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["RegistrationConnectionString"].ConnectionString);
            conn.Open();
            string insertQuery = "insert into UserData(Username,Firstname,Lastname,Email,Password,CustomerType,DeliveryAddress,Zip,ContactNumber)values(@Username,@Firstname,@Lastname,@Email,@Password,@CustomerType,@DeliveryAddress,@Zip,@ContactNumber)";
            SqlCommand scm = new SqlCommand(insertQuery, conn);
            scm.Parameters.AddWithValue("@Username", txtUser.Text);
            scm.Parameters.AddWithValue("@Firstname", txtFN.Text);
            scm.Parameters.AddWithValue("@Lastname", txtLN.Text);
            scm.Parameters.AddWithValue("@Email", txtEmail.Text);
            scm.Parameters.AddWithValue("@Password", BusinessLayer.ShoppingCart.CreateSHAHash(txtPW.Text));
            scm.Parameters.AddWithValue("@CustomerType", RadioButtonList1.SelectedItem.ToString());
            scm.Parameters.AddWithValue("@DeliveryAddress", txtAddress.Text);
            scm.Parameters.AddWithValue("@Zip", txtZip.Text);
            scm.Parameters.AddWithValue("@ContactNumber", txtContact.Text);

            scm.ExecuteNonQuery();
            Session["Contact"]= txtContact.Text;
            Session["Email"] = txtEmail.Text;
            Session["DeliveryAddress"] = txtAddress.Text;
            label_register_success.Text = ("Registration Successful!");
            //Response.Redirect("Home.aspx");
            conn.Close();
        }
        catch (Exception ex)
        {
            Response.Write("Error:" + ex.ToString());
        }
    }

Answer 1

您验证Page_Load上的数据吗？ 我认为，您可以选择这些解决方案

1. 在插入数据之前，必须在btn_Registration_Click中完成此操作，或者
2. 也许，您可以将其修改为在sp中执行，如果数据重复则通过它抛出消息并在那里进行检查。

应该是这样（根据解决方案1）

protected void Page_Load(object sender, EventArgs e)
    {
        if (IsPostBack)
        {
        }
    }
    protected void btn_Registration_Click(object sender, EventArgs e)
    {
        try
        {
            SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["RegistrationConnectionString"].ConnectionString);
            conn.Open();
            string checkuser = "select count(*) from UserData where Username = '" + txtUser.Text + "'";
            SqlCommand scm = new SqlCommand(checkuser, conn);
            int temp = Convert.ToInt32(scm.ExecuteScalar().ToString());
            if (temp > 0) // check if user already exist.
            {
                Response.Write("User already existing");
            }
            else
            {
                string insertQuery = "insert into UserData(Username,Firstname,Lastname,Email,Password,CustomerType,DeliveryAddress,Zip,ContactNumber)values(@Username,@Firstname,@Lastname,@Email,@Password,@CustomerType,@DeliveryAddress,@Zip,@ContactNumber)";
                scm = new SqlCommand(insertQuery, conn);
                scm.Parameters.AddWithValue("@Username", txtUser.Text);
                scm.Parameters.AddWithValue("@Firstname", txtFN.Text);
                scm.Parameters.AddWithValue("@Lastname", txtLN.Text);
                scm.Parameters.AddWithValue("@Email", txtEmail.Text);
                scm.Parameters.AddWithValue("@Password", BusinessLayer.ShoppingCart.CreateSHAHash(txtPW.Text));
                scm.Parameters.AddWithValue("@CustomerType", RadioButtonList1.SelectedItem.ToString());
                scm.Parameters.AddWithValue("@DeliveryAddress", txtAddress.Text);
                scm.Parameters.AddWithValue("@Zip", txtZip.Text);
                scm.Parameters.AddWithValue("@ContactNumber", txtContact.Text);

                scm.ExecuteNonQuery();
                Session["Contact"]= txtContact.Text;
                Session["Email"] = txtEmail.Text;
                Session["DeliveryAddress"] = txtAddress.Text;
                label_register_success.Text = ("Registration Successful!");
                //Response.Redirect("Home.aspx");
            }
            conn.Close();
        }
        catch (Exception ex)
        {
            Response.Write("Error:" + ex.ToString());
        }
    }