C# 空连接-连接到ASP.NET-Microsoft SQL Server

我一直在尝试连接到数据库，但它显示“null”错误。 所以 我试着打开我练习的前一张表格，结果是非常好的

这是我的代码：

string username = txtusername.Text;
        string firstname = txtfirstname.Text;
        string lastname = txtlastname.Text;
        string email = txtemail.Text;
        string password = txtpass.Text;
        string gender = rbgender.Text;
        string nationality = dcountry.Text;
        string phone = txtphone.Text;

        string connection = ConfigurationManager.ConnectionStrings["connectionString"].ConnectionString;
        SqlConnection connect = new SqlConnection(connection);
        string command = "INSERT INTO Persons(username, firstname, lastname, email, password, gender, nationality, phone) VALUES('@username','@firstname','@lastname','@email','@password','@gender','@nationality','@phone')";


        SqlCommand insert = new SqlCommand(command +","+ connection);
        insert.Parameters.AddWithValue("@username", username);
        insert.Parameters.AddWithValue("@firstname", firstname);
        insert.Parameters.AddWithValue("@lastname", lastname);
        insert.Parameters.AddWithValue("@email", email);
        insert.Parameters.AddWithValue("@password", password);
        insert.Parameters.AddWithValue("@gender", gender);
        insert.Parameters.AddWithValue("@nationality", nationality);
        insert.Parameters.AddWithValue("@phone", phone);
        insert.ExecuteNonQuery();
        connect.Close();

它是否与web.config中的ConnectionString有关

 <connectionStrings>
<add name="ApplicationServices"
     connectionString="Data Source=ADRIAN-LAPTOP\SQL;Initial Catalog=New;Integrated Security=True"
     providerName="System.Data.SqlClient" />

web.config文件中的键与代码中使用的键不同

应该是,

string connection = ConfigurationManager.ConnectionStrings["ApplicationServices"]
                                        .ConnectionString;

并且不需要将参数名称包装在单引号中

 string command = @"
   INSERT INTO Persons
      (username, firstname, lastname, email, password, gender, nationality,phone) 
     VALUES
      (@username,@firstname,@lastname,@email,@password,@gender,@nationality,@phone)";

请注意，始终通过使用语句或调用dispose来处置ADO资源

---

请让我们知道您正面临什么样的异常。您能否添加一个try-catch，并接受异常，因为这样更容易知道到底发生了什么。除了其他人已经说过的以外，SqlCommand-insert=new-SqlCommandcommand+，+connection；应为SqlCommand insert=new SqlCommandcommand，connection；。或者更好的是，用。。。{…}哇，谢谢你。我还注意到我实际上收到了一个错误，我忘记打开连接。除息的

using(SqlConnection connect = new SqlConnection(connectionString))
 {
  //
 }