Error displaying info from 2 linked tables using Entity Framework Core

Question

I am following a tutorial and getting an error that the tutorial doesn't when trying to use the foreign key to pull data from a second table to display in my MVC display. I am using the following code, and get the following error. Can anyone help point me in the right direction as I cant see anything wrong.

System.InvalidOperationException: 'There is already an open DataReader associated with this Connection which must be closed first.'

This exception was originally thrown at this call stack:

[External Code] InAndOut.Controllers.ExpenseController.Index() in ExpenseController.cs [External Code]

Code:

using Microsoft.AspNetCore.Mvc;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using InAndOut.Data;
using InAndOut.Models;
using InAndOut.Models.ViewModels;
using Microsoft.AspNetCore.Mvc.Rendering;

namespace InAndOut.Controllers
{
    public class ExpenseController : Controller
    {
        private readonly ApplicationDbContext _db;

        public ExpenseController(ApplicationDbContext db)
        {
            _db = db;
        }

        public IActionResult Index()
        {
            IEnumerable<Expense> objList = _db.Expenses;

            foreach (var obj in objList)
            {
                obj.ExpenseType = _db.ExpenseTypes.FirstOrDefault(u => u.Id == obj.ExpenseTypeId);
            }
            return View(objList);
        }

        //Get-Create
        public IActionResult Create()
        {
            ExpenseVM expenseVm = new ExpenseVM()
            {
                Expense = new Expense(),
                TypeDropDown = _db.ExpenseTypes.Select(i => new SelectListItem
                {
                    Text = i.Name,
                    Value = i.Id.ToString()
                })
            };

            return View(expenseVm);
        }

        //Post-Create
        [HttpPost]
        [ValidateAntiForgeryToken]
        public IActionResult Create(ExpenseVM obj)
        {
            if (ModelState.IsValid)
            {
                //obj.ExpenseTypeId = 3;
                _db.Expenses.Add(obj.Expense);
                _db.SaveChanges();
                return RedirectToAction("Index");
            }

            return View(obj);
        }

        //Get Delete
        public IActionResult Delete(int? id)
        {
            if (id == null || id == 0)
            {
                return NotFound();
            }

            var obj = _db.Expenses.Find(id);

            if (obj == null)
            {
                return NotFound();
            }

            return View(obj);
        }

        //Post-Delete
        [HttpPost]
        [ValidateAntiForgeryToken]
        public IActionResult DeletePost(int? id)
        {
            var obj = _db.Expenses.Find(id);

            if (obj == null)
            {
                return NotFound();
            }

            _db.Expenses.Remove(obj);
            _db.SaveChanges();
            return RedirectToAction("Index");
        }

        //Get Update
        public IActionResult Update(int? id)
        {
            if (id == null || id == 0)
            {
                return NotFound();
            }

            var obj = _db.Expenses.Find(id);

            if (obj == null)
            {
                return NotFound();
            }

            return View(obj);
        }

        //Post-Create
        [HttpPost]
        [ValidateAntiForgeryToken]
        public IActionResult Update(Expense obj)
        {
            if (ModelState.IsValid)
            {
                _db.Expenses.Update(obj);
                _db.SaveChanges();
                return RedirectToAction("Index");
            }

            return View(obj);
        }
    }
}