Asp.net System.NullReferenceException when creating new MysqlConnection-CodePudding

`I'm new to asp.net and when I tried to connect to MySQL database I got this error. error message

here is my code in web.config file

<configuration>

  <appSettings>
    
      <add key="HostPrefix" value="/root" />
      <add key="ServerIp" value="localhost" />
      <add key="MysqlConnectionstring" value="server=localhost;Database=world;port=3306;user=root;password=1234;SslMode=none" />
      <add key="UserImagePath" value="world\city\" />
      
  </appSettings>

here is my code for database connection

using Common;
using MySql.Data.MySqlClient;
using System;
using System.Data;
using System.Data.SqlClient;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Web.Configuration;

namespace Repositories
{
    public class StudentRepository
       
    {
         private string ConnectionstringMaster = WebConfigurationManager.AppSettings["MysqlConnectionString"];

  private static readonly NLog.Logger Logger = NLog.LogManager.GetCurrentClassLogger();        
       
public studentsModel UserRegistration(string Id )
        { studentsModel stud1 = new studentsModel();     

try
             {
string Query = "select ID,Name,CountryCode,District from world.city where ID='"   Id   "'";
using (var connection = new MySqlConnection(ConnectionstringMaster))
                 
                 {
                      using (var command= new MySqlCommand(Query,connection))
                      {
                          connection.Open();
                          using (var sdr=command.ExecuteReader())
                          {
                              while (sdr.Read())
                              {
                                  
                                  stud1.FirstName = sdr["Name"].ToString();

                              }

                          }
                      }
                  }
                  return stud1;
                
                
            }
            catch (Exception e)
             {
                Logger.Info("inside Exception Repo Userregistration  " e.ToString());
              
                return stud1;
             } 
            

           
        }
    }
}

Here I'm trying to get data from database and assign those values to studentmodel stud1 . But when I try to create new MySQL connection with my database in localhost it gives exception like this .

ispasswordExpired :connection.ispasswordExpired threw an exception of type 'System.nullReferenceException'

ServerThread :connection.ServerThread threw an exception of type 'System.nullReferenceException'

ServerVersion : connection.ServerVersion threw an exception of type 'System.nullReferenceException'

CodePudding user response：

You first need to add the connectionStrings section in your web.config file and remove it from the appSettings section like this:

<configuration>

  <connectionStrings>
    <add name="MysqlConnectionstring" connectionString="server=localhost;Database=world;port=3306;user=root;password=1234;SslMode=none" />
  </connectionStrings>
  
  <appSettings>  
      <add key="HostPrefix" value="/root" />
      <add key="ServerIp" value="localhost" />
      <add key="" value="" />
      <add key="UserImagePath" value="world\city\" />   
  </appSettings>
 
</configuration>

And then you can access the connection string value by accessing the ConnectionString property in your code like this:

private string ConnectionstringMaster = ConfigurationManager.ConnectionStrings["MysqlConnectionstring"].ConnectionString;

CodePudding user response：

You need to add a connectionStrings to your Web.Config.

Web.config:

<configuration>
  <connectionStrings>
    <add name="MysqlConnectionstring" connectionString="Server=myServerName;Port=3306;Database=myDatabaseName;Uid=testUser;Pwd=myPassword;" />      
  </connectionStrings>
                     ...
</configuration>