why i got error "Object reference not set to an instance of an object" with session parameter and its not null?

Question

I am new to mvc and i want to build new system , i made login screen and i save the login informations in Session parameter then redirect to another window ,

when i use SELECT statement without compare session value its working without any error and this is the controller code:

public ActionResult Index()
        {
            string sql= @"SELECT PATIENT_NO , LAB_ORDER_NO , PATIENT_NAME_A , SERV_REQUEST_DATE_G , 
                               SERV_REQUEST_DOCTOR_NAME 
                             FROM LAB_ORDERS_STS where  PATIENT_NO=10  ";


            DataTable dt = func.fireDatatable(string.Format(sql));
            return View(dt);

        }

but when i use the session and get data depending on session["MRN"] i got the error "Object reference not set to an instance of an object" and this is the code :

public ActionResult Index()
        {
            string sql= @"SELECT PATIENT_NO , LAB_ORDER_NO , PATIENT_NAME_A , SERV_REQUEST_DATE_G , 
                               SERV_REQUEST_DOCTOR_NAME 
                             FROM LAB_ORDERS_STS where 1=1 ";

           string condition = "";
            string orderby = "LAB_ORDERS_STS.LAB_ORDER_NO desc";
            condition += " and LAB_ORDERS_STS.PATIENT_NO ='" + Session["MRN"] + "'";


            DataTable dt = func.fireDatatable(string.Format(sql+condition+orderby));
            return View(dt);

        } 

This is also the login controller code :

[HttpPost]
        public ActionResult Authorise(kaashtaif.Models.WEBSITE_USERS usermodel)
        {
            using (Entities db = new Entities())
            {
                var userdetails = db.WEBSITE_USERS.Where(x => x.ID_NO == usermodel.ID_NO && x.MOBILE == usermodel.MOBILE && x.PATIENT_NO == usermodel.PATIENT_NO).FirstOrDefault();
                if (userdetails == null)
                {
                    usermodel.LoginErrorMessage = "Entered Data Not Exist Please Update your Data - البيانات المدخلة غير صحيحة ارجو تحديث بيانات الملف الطبي";
                    return View("Login", usermodel);
                }
                else
                {
                    Session["IDNO"] = usermodel.ID_NO;
                    Session["MOBILE"] = usermodel.MOBILE;
                    Session["MRN"] = usermodel.PATIENT_NO;
                    return RedirectToAction("Index", "Result");
                }
            }

        }

I debug the code and session parameters save value and not null .

This is the Index.cshtml code :

@model System.Data.DataTable

@{
    ViewBag.Title = "Index";
}

<h2>نتائج تحاليل المختبر </h2>

<table class="table">
    <tr>
        <th> PATIENT NO </th>
        <th>
            ORDER NO
        </th>
        <th>
            PATIENT NAME
        </th>
        <th>
            REQUEST DATE
        </th>
        <th>
            DOCTOR NAME
        </th>
    </tr>

    @foreach (System.Data.DataRow dr in Model.Rows)
    {
        <tr>
            <td>@dr["PATIENT_NO"].ToString()</td>
            <td>@dr["LAB_ORDER_NO"].ToString()</td>
            <td>@dr["PATIENT_NAME_A"].ToString()</td>
            <td>@dr["SERV_REQUEST_DATE_G"].ToString()</td>
            <td>@dr["SERV_REQUEST_DOCTOR_NAME"].ToString()</td>
            <td>@Html.ActionLink("Details", "Details", new { /* id=item.PrimaryKey */ }) </td>
        </tr>
    }

</table>
<p>
    @Html.ActionLink("Edit", "Edit", new { /* id = Model.PrimaryKey */ }) |
    @Html.ActionLink("Back to List", "Index")
</p>

Finally the error appeared on this line foreach loop and when i use Session["MRN"] but when i select data direct without session parameter its working , what is the mistake ? Also i checked the posts in the site but no solution to my case.

@foreach (System.Data.DataRow dr in Model.Rows)

Answer 1

You miss the Order by in the string orderby = "LAB_ORDERS_STS.LAB_ORDER_NO desc"; To solve the problem, change the orderby to:

string orderby = " Order by LAB_ORDERS_STS.LAB_ORDER_NO desc";