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

Question

我一直在尝试连接到数据库，但它显示“null”错误。 所以， 我尝试打开之前练习的表格，结果非常好。

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();

和web.config中的connectionstrings有关系吗？

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

Answer 1

web.config 文件中的键与在代码中使用的不同。

应该是，

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

并且无需将参数名称用单引号括起来。

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

附带说明，始终使用using 语句（或调用Dispose()）来处理ADO 资源。

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