How do I remove an error:An exception of type 'System.NullReferenceException' occurred in ADO_MVC.dll but was not handled in user code

Question

1.00/5 (1 vote)

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C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Configuration;
using System.Data.SqlClient;

namespace ADO_MVC
{
    public class ADOMVC
    {       
        public int Insert(string query)
        {
            SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["con_String"].ToString());
            conn.Open();
            SqlCommand cmd = new SqlCommand();
            cmd.Connection = conn;
            cmd.CommandText = query;
            int res = cmd.ExecuteNonQuery();
            conn.Close();
            return res;
        }
    }
}

Note : The error is given in SqlConnection ("con_String")

Posted 6-Oct-15 2:24am

Member 11392252

Updated 6-Oct-15 2:43am

Naveen.Sanagasetti

v2

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Member 11392252 6-Oct-15 8:26am

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;

namespace ADO_MVC.Controllers
{
public class HomeController : Controller
{
public ActionResult Index()
{
ViewBag.Message = "Modify this template to jump-start your ASP.NET MVC application.";

return View();
}
public ActionResult InsertResult()
{
ADO_MVC.Models.Info data = new Models.Info();
data.Fname = Request["fname"];
data.Lname = Request["lname"];

int res = data.Insert();
if(res>0)
{
Response.Write("Insert Successfull....");

}
else
{
return RedirectToAction("Index", "Home");
}
return View();
}

public ActionResult About()
{
ViewBag.Message = "Your app description page.";

return View();
}

public ActionResult Contact()
{
ViewBag.Message = "Your contact page.";

return View();
}
}
}
This is the HomeController

@model ADO_MVC.Models.Info
@{
ViewBag.Title = "InsertResult";
}

InsertResult

<html>
<body>
@using (Html.BeginForm("InsertResult", "Home"))
{
<fieldset>
My Information
<table>
<tr>
<td>@Html.LabelFor(model => model.ID)</td>
<td>@Html.TextBox("id")</td>
</tr>
<tr>
<td>@Html.LabelFor(model => model.Fname)</td>
<td>@Html.TextBox("fname")</td>
</tr>
<tr>
<td>@Html.LabelFor(model => model.Lname)</td>
<td>@Html.TextBox("lname")</td>
</tr>
<tr>
<td>@Html.TextBox("btn_submit", "Insert Data", new { type = "submit" })</td>
</tr>
</table>
</fieldset>
}

</body>
</html>
This is the Index Page

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace ADO_MVC.Models
{
public class Info
{
public int ID { get; set; }
public string Fname { get; set; }
public string Lname { get; set; }

public int Insert(Info data)
{
string query = "insert into myinfo values('"+data.Fname+"','"+data.Lname+"')";
ADOMVC ado = new ADOMVC();
int res = ado.Insert(query);
return res;
}
public int Insert()
{
string query = "insert into myinfo values('" + Fname + "','" + Lname + "')";
ADOMVC ado = new ADOMVC();
int res = ado.Insert(query);
return res;
}

}

}
And this is the Model Info.cs

ZurdoDev 6-Oct-15 8:31am

Which line of code causes it?

Member 11392252 6-Oct-15 8:33am

In SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["con_String"].ToString());
(Here)

ZurdoDev 6-Oct-15 8:40am

Then ConfigurationManager.ConnectionStrings["con_String"] is null.

F-ES Sitecore 6-Oct-15 8:49am

Check the connection string is defined in the right place, ie the web.config file in the site root. If your code is in a separate project that projects app.config file is NOT used.

Richard Deeming 6-Oct-15 9:28am

The design of your method suggests that you're writing code which is vulnerable to SQL Injection:

Everything you wanted to know about SQL injection (but were afraid to ask) | Troy Hunt[^]
How can I explain SQL injection without technical jargon? | Information Security Stack Exchange[^]
Query Parameterization Cheat Sheet | OWASP[^]
SQL injection attack mechanics | Pluralsight [^]

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Naveen.Sanagasetti · Answer 1 · 2015-10-06T02:46:00

Solution 1

Check whether connection string configured properly or not in web.config, in your case it return null that is the reason it's throwing null reference error. Please debug the program and check line by line and found the issue.

Posted 6-Oct-15 2:46am

Naveen.Sanagasetti

Comments

Member 11392252 6-Oct-15 9:06am

<add name="ADO_mvc" connectionstring="Data source=.\sqlexpress; Initial Catalog=ADO_mvc; Integrated Security=true ">
This is my Connection string.