why viewmodel can't get data from database?even though it return values

Question

I have a view model class Paymentcart and inside that I have created object of another two classes payment and cart.

Class Paymentcart

namespace Temple.Models
{
    public class paymentcart
    {
        public cart cart { get; set; }
        public payment payment { get; set; }
    }
}

Class cart:

public class cart
{
         public long cid { get; set; }
         public long vid { get; set; }
         public long userid { get; set; }
         public long count { get; set; }
         public long tempid { get; set; }
         public string  name { get; set; }
         public string star { get; set; }
         public string dates { get; set; }
         public string vname { get; set; }
         public string vrate { get; set; }
         public string totalamount { get; set; }
         public int rows { get; set; }
}

Class payment:

public class payment
{
        public long cid { get; set; }
        public long vid { get; set; }
        public long userid { get; set; }

        public long tempid { get; set; }
        public string amt { get; set; }
        public string cname { get; set; }
        public long number { get; set; }
        public long securitycode { get; set; }
        public string expdate { get; set; }
        public string totalamount { get; set; }
}

But when I am putting value from the database, it shows "Null Exception" error (but the database does return values).

This is the controller code:

 List<paymentcart> qlist = new List<paymentcart>();
            using (SqlConnection con = new SqlConnection(connectionString))
            {
                using (SqlCommand cmd = new SqlCommand("getcart", con))
                {
                    cmd.CommandType = CommandType.StoredProcedure;
                      var q = new paymentcart();
                    q.cart = new cart();
                    cmd.Parameters.AddWithValue("@uid", uid);
                    con.Open();
                    SqlDataReader rd = cmd.ExecuteReader();
                    while (rd.Read())
                    {
                         q.cart.tempid = Convert.ToInt64(rd["TdId"]);
                          q.cart.userid  = Convert.ToInt32(rd["UserID"]);
                           q.cart.cid = Convert.ToInt32(rd["cid"]);
                           q.cart. vid = Convert.ToInt32(rd["v_id"]);
                            q.cart.name = Convert.ToString(rd["name"]);
                           q.cart. star = Convert.ToString(rd["star"]);
                           q.cart. dates = Convert.ToString(rd["dates"]);
                            q.cart.vname = Convert.ToString(rd["vname"]);
                           q.cart. vrate = Convert.ToString(rd["vrate"]);
                           qlist.Add(q);

                    }

                }

            }
            return qlist;

I have attached a screenshot here: Error Page

I don't know am using the correct method; please help me to solve this.

Possible duplicate of [What is a NullReferenceException, and how do I fix it?](https://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — Joelius, Jul 06 '19 at 08:57
@Joelius ,I have checked this ,bt cant find the answer through that question,I feel different — codeseeker, Jul 06 '19 at 09:47

Prasad Telkikar · Answer 1 · 2019-07-06T08:58:23.393

2

You created instance of paymentcart, that is correct but you missed to create instance of cart class, while instantiating paymentcart class object, create object of cart class

something like

 var q = new paymentcart();
 q.cart = new Cart(); //This will resolve error related to object instantiation
 //^^^ This was missing, I used naming conventions to differentiate between class name and object name 
 //Your code goes here
 cmd.Parameters.AddWithValue("@uid", uid);
 con.Open();
 SqlDataReader rd = cmd.ExecuteReader();

Bonus : Always follow naming conventions to declare class name, property name and variable names

Your class name should start with Capital letter i.e. PascalCase
Your variable name should start with small letter i.e. camelCase

edited Jul 06 '19 at 08:58

answered Jul 06 '19 at 08:50

Prasad Telkikar

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Thnq sir,Bu t while displaying this values using a forloop ,It retuns only the last value in the list – codeseeker Jul 06 '19 at 11:25
You need to add each record to the list of PaymentCart i.e. `qList.Add(q);` – Prasad Telkikar Jul 06 '19 at 11:50
i didn't mean this scenario sir .This works fine,But when am displaying the data it returns last value only – codeseeker Jul 06 '19 at 11:53
Can you add another question where you will mention scenario which explain your implementation of display function, because your current question does not contain any information related to view – Prasad Telkikar Jul 06 '19 at 12:02
even though i have put this code inside while loop,It overwrites .How to overcome this?please help me – codeseeker Jul 06 '19 at 13:42
I can't help you here as I need to debug full code and need to check what is going wrong in your code, If you have any git repository which I can look into then provide. Sorry I can't help here just looking into your question why this code is not working – Prasad Telkikar Jul 06 '19 at 13:45
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/196077/discussion-between-prasad-telkikar-and-codeseeker). – Prasad Telkikar Jul 06 '19 at 14:38

score 0 · Accepted Answer · answered Jul 06 '19 at 14:21

Please try below code:

public List<paymentcart> ViewCart(int uid)
        {
            List<paymentcart> qlist = new List<paymentcart>();
            using (SqlConnection con = new SqlConnection(connectionString))
            {

                using (SqlCommand cmd = new SqlCommand("getcart", con))
                {
                    cmd.CommandType = CommandType.StoredProcedure;

                    cmd.Parameters.AddWithValue("@uid", uid);
                    con.Open();
                    SqlDataReader rd = cmd.ExecuteReader();

                    while (rd.Read())
                    {
                        var q = new paymentcart();
                        q.cart = new cart();

                         q.cart.tempid = Convert.ToInt64(rd["TdId"]);
                          q.cart.userid  = Convert.ToInt32(rd["UserID"]);
                           q.cart.cid = Convert.ToInt32(rd["cid"]);
                           q.cart. vid = Convert.ToInt32(rd["v_id"]);
                            q.cart.name = Convert.ToString(rd["name"]);
                           q.cart. star = Convert.ToString(rd["star"]);
                           q.cart. dates = Convert.ToString(rd["dates"]);
                            q.cart.vname = Convert.ToString(rd["vname"]);
                           q.cart. vrate = Convert.ToString(rd["vrate"]);
                           qlist.Add(q);




                    }

                }

            }
            return qlist;
        }

why viewmodel can't get data from database?even though it return values

2 Answers2