c# MVC "object reference not set to an instance of an object" Yet the UserId has a value

Question

I've got a null reference error. My code is below, the error points to the 'return user.Applications.ToList();' of GetApplications method. Any tips how to fix it would be greatly appreciated.

UserDAO:

using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using NAA.Data.IDAO;
using NAA.Data.Models.Domain;
using NAA.Data.Repository;


namespace NAA.Data.DAO
{
    public class UserDAO : IUserDAO
    {

        public User GetUser(string Userid, NAAContext context)
        {
            return context.Users.Find(Userid);
        }
        public void AddUniversityToCollection(Application application, University university, NAAContext context)
        {
            context.Universities.Find(university.UniversityId).Applications.Add(application);
        }


        public void AddUser(User user, NAAContext context)
        {
            context.Users.Add(user);
            context.SaveChanges();

        }
        public IList<Application> GetApplications(string UserId, NAAContext context)
        {
            context.Users.Include(g => g.Applications).ToList();
            User user = context.Users.Find(UserId);
            return user.Applications.ToList();
        }

        public void AddUniversityToCollection(Application newApplication, User user, NAAContext context)
        {
            context.Applications.Find(newApplication.ApplicationId);
        }
    }
}

IUserDAO: I doubt the problem is here

using NAA.Data.Models.Domain;
using NAA.Data.Repository;
using NAA.Data.DAO;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace NAA.Data.IDAO
    
{
    public interface IUserDAO
    {
        void AddUser(User user, NAAContext context);
        User GetUser(string userID, NAAContext context);
        void AddUniversityToCollection(Application newApplication, User user, NAAContext context);
        IList<Application> GetApplications(string UserId, NAAContext context);
    }
}

UserService:

using NAA.Data.Models.Domain;
using NAA.Data.Repository;
using NAA.services.IService;
using NAA.services.Models;
using NAA.Data.DAO;
using NAA.Data.IDAO;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace NAA.services.Service
{
    public class UserService : IUserService
    {
        private IUserDAO userDAO;
        public UserService()
        {
            userDAO = new UserDAO();
        }
        public void AddUser(User newUser)
        {
         
       using (var context = new NAAContext())
            {
                userDAO.AddUser(newUser, context);
            }
        }



        public User GetUser(string userId)
        {
            using (NAAContext context = new NAAContext())
            {
                return context.Users.Find(userId);
            }
       
            }
        public IList<Application>GetApplications(string UserId)
        {
            using (var context = new NAAContext())
            {
                return userDAO.GetApplications(UserId, context);
            }
        }
            }


                
        }

IUserService:

using NAA.Data.Models.Domain;
using NAA.Data.Repository;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using NAA.services.IService;
using NAA.services.Service;
using NAA.services.Models;

namespace NAA.services.IService
{
    public interface IUserService
    {
        User GetUser(string userId);
        void AddUser(User newUser);
        IList<Application> GetApplications(string UserId);
    }

}

UserController:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using NAA.services.IService;
using NAA.services.Service;
using NAA.Data.Models.Domain;
using NAA.Data.Repository;
using NAA.services.Models;

namespace NAA.Controllers
{
    public class UserController : Controller
    {
        IUserService UserService;
        public UserController()
        {
            UserService = new UserService();
        }

        // GET: User
        public ActionResult AddUser() //string userId, string email (add later)
        {
            return View();
        }

           // POST: User/Create
           [HttpPost]
        public ActionResult AddUser(User newUser, NAAContext context)
        {
            try
            {
                // TODO: Add insert logic here
                UserService.AddUser(newUser);
                return RedirectToAction("GetUser", "User", new {id = newUser.UserId });
            }
            catch
            {
                return RedirectToAction("GetUser", "User", new { id = newUser.UserId });
            }
        }  
        public ActionResult GetUser(string id)
        {
            return View(UserService.GetUser(id));
        }

        public ActionResult GetApplications(string UserId)
            {
            return View(UserService.GetApplications(UserId));
            }
        // GET: User/Details/5
        // GET: User/Create
        public ActionResult Create()
        {
            return View();
        }

        // POST: User/Create
        [HttpPost]
   

        // GET: User/Edit/5
        public ActionResult Edit(int id)
        {
            return View();
        }

        // POST: User/Edit/5
        [HttpPost]
        public ActionResult Edit(int id, FormCollection collection)
        {
            try
            {
                // TODO: Add update logic here

                return RedirectToAction("Index");
            }
            catch
            {
                return View();
            }
        }

        // GET: User/Delete/5
        public ActionResult Delete(int id)
        {
            return View();
        }

        // POST: User/Delete/5
        [HttpPost]
        public ActionResult Delete(int id, FormCollection collection)
        {
            try
            {
                // TODO: Add delete logic here

                return RedirectToAction("Index");
            }
            catch
            {
                return View();
            }
        }
    }
}

GetApplications view:

@model IEnumerable<NAA.Data.Models.Domain.Application>

@{
    ViewBag.Title = "GetApplications";
}

<h2>GetApplications</h2>

<p>
    @Html.ActionLink("Create New", "Create")
</p>
<table class="table">
    <tr>
        <th>
            @Html.DisplayNameFor(model => model.Course)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.Statement)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.TeacherContact)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.TeacherReference)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.Firm)
        </th>
        <th></th>
    </tr>

@foreach (var item in Model) {
    <tr>
        <td>
            @Html.DisplayFor(modelItem => item.Course)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.Statement)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.TeacherContact)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.TeacherReference)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.Firm)
        </td>
        <td>
            @Html.ActionLink("Edit", "Edit", new { id=item.ApplicationId }) |
            @Html.ActionLink("Details", "Details", new { id=item.ApplicationId }) |
            @Html.ActionLink("Delete", "Delete", new { id=item.ApplicationId })
        </td>
    </tr>
}

</table>

Thank you in advance guys I'm really struggling with this and I can't work out how I'd fix it.

EDIT!

Application class:

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace NAA.Data.Models.Domain
{
   
    public class Application
    {
        [Key]
        public int ApplicationId { get; set; }
        public string Course { get; set; }
        public string Statement { get; set; }
        public string TeacherContact { get; set; }
        public string TeacherReference { get; set; }
        public char Offer { get; set; }
        public bool Firm { get; set; }
    }
}

User class:

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace NAA.Data.Models.Domain
{
    public class User
    {
        [Key]
        public string UserId { get; set; }
        public string Name { get; set; }
        
        public string Address { get; set; }
        public string Phone { get; set; }
        public string Email { get; set; }
        public virtual ICollection<Application> Applications { get; set; }
        public virtual ICollection<University> Universities { get; set;}
    }
}

Could you show your User and Applicatons classes, pls? – Serge Feb 20 '21 at 16:25 — Serge, Feb 20 '21 at 16:25

Serge · Answer 1 · 2021-02-20T17:27:26.113

0

Try to change your action:

public IEnumerable<Application> GetApplications(string UserId, NAAContext context)
        {
               var user =context.Users
                    .Include(a => a.Applications)
                     .Where (u=> u.UserId==UserId)
                      .FirstOrDefault();
             
            return user.Applications;
         }

edited Feb 20 '21 at 17:27

answered Feb 20 '21 at 16:24

Serge

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Hi Sergey, I've edited to include my user and application methods, the user class has collection of methods that Im trying display, that return context line didn't work unfortunately as applications doesn't contain Userid – George Turner Feb 20 '21 at 16:50
Thanks, but do you have UserApplication class? How User and Applications are related? I quess it's many to many. – Serge Feb 20 '21 at 17:22

c# MVC "object reference not set to an instance of an object" Yet the UserId has a value

1 Answers1