StudentsController.cs

#define SortFilterPage //or ScaffoldedIndex or SortOnly or SortFilter or DynamicLinq
#define ReadFirst //or CreateAndAttach
#define DeleteWithReadFirst // or DeleteWithoutReadFirst

using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.EntityFrameworkCore;
using ContosoUniversity.Data;
using ContosoUniversity.Models;
using System;
using Microsoft.Extensions.Logging;

// <snippet_Context>
namespace ContosoUniversity.Controllers
{
    public class StudentsController : Controller
    {
        private readonly SchoolContext _context;

        public StudentsController(SchoolContext context)
        {
            _context = context;
        }
// </snippet_Context>

        // GET: Students

#if (ScaffoldedIndex)
// <snippet_ScaffoldedIndex>
        public async Task<IActionResult> Index()
        {
            return View(await _context.Students.ToListAsync());
        }
// </snippet_ScaffoldedIndex>
#elif (SortOnly)
// <snippet_SortOnly>
        public async Task<IActionResult> Index(string sortOrder)
        {
            ViewData["NameSortParm"] = String.IsNullOrEmpty(sortOrder) ? "name_desc" : "";
            ViewData["DateSortParm"] = sortOrder == "Date" ? "date_desc" : "Date";
            var students = from s in _context.Students
                           select s;
            switch (sortOrder)
            {
                case "name_desc":
                    students = students.OrderByDescending(s => s.LastName);
                    break;
                case "Date":
                    students = students.OrderBy(s => s.EnrollmentDate);
                    break;
                case "date_desc":
                    students = students.OrderByDescending(s => s.EnrollmentDate);
                    break;
                default:
                    students = students.OrderBy(s => s.LastName);
                    break;
            }
            return View(await students.AsNoTracking().ToListAsync());
        }
// </snippet_SortOnly>
#elif (SortFilter)
// <snippet_SortFilter>
        public async Task<IActionResult> Index(string sortOrder, string searchString)
        {
            ViewData["NameSortParm"] = String.IsNullOrEmpty(sortOrder) ? "name_desc" : "";
            ViewData["DateSortParm"] = sortOrder == "Date" ? "date_desc" : "Date";
            ViewData["CurrentFilter"] = searchString;

            var students = from s in _context.Students
                           select s;
            if (!String.IsNullOrEmpty(searchString))
            {
                students = students.Where(s => s.LastName.Contains(searchString)
                                       || s.FirstMidName.Contains(searchString));
            }
            switch (sortOrder)
            {
                case "name_desc":
                    students = students.OrderByDescending(s => s.LastName);
                    break;
                case "Date":
                    students = students.OrderBy(s => s.EnrollmentDate);
                    break;
                case "date_desc":
                    students = students.OrderByDescending(s => s.EnrollmentDate);
                    break;
                default:
                    students = students.OrderBy(s => s.LastName);
                    break;
            }
            return View(await students.AsNoTracking().ToListAsync());
        }
// </snippet_SortFilter>
#elif (SortFilterPage)
// <snippet_SortFilterPage>
        public async Task<IActionResult> Index(
            string sortOrder,
            string currentFilter,
            string searchString,
            int? pageNumber)
        {
            ViewData["CurrentSort"] = sortOrder;
            ViewData["NameSortParm"] = String.IsNullOrEmpty(sortOrder) ? "name_desc" : "";
            ViewData["DateSortParm"] = sortOrder == "Date" ? "date_desc" : "Date";

            if (searchString != null)
            {
                pageNumber = 1;
            }
            else
            {
                searchString = currentFilter;
            }

            ViewData["CurrentFilter"] = searchString;

            var students = from s in _context.Students
                           select s;
            if (!String.IsNullOrEmpty(searchString))
            {
                students = students.Where(s => s.LastName.Contains(searchString)
                                       || s.FirstMidName.Contains(searchString));
            }
            switch (sortOrder)
            {
                case "name_desc":
                    students = students.OrderByDescending(s => s.LastName);
                    break;
                case "Date":
                    students = students.OrderBy(s => s.EnrollmentDate);
                    break;
                case "date_desc":
                    students = students.OrderByDescending(s => s.EnrollmentDate);
                    break;
                default:
                    students = students.OrderBy(s => s.LastName);
                    break;
            }

            int pageSize = 3;
            return View(await PaginatedList<Student>.CreateAsync(students.AsNoTracking(), pageNumber ?? 1, pageSize));
        }
// </snippet_SortFilterPage>
#elif (DynamicLinq)
// <snippet_DynamicLinq>
        public async Task<IActionResult> Index(
            string sortOrder,
            string currentFilter,
            string searchString,
            int? pageNumber)
        {
            ViewData["CurrentSort"] = sortOrder;
            ViewData["NameSortParm"] = 
                String.IsNullOrEmpty(sortOrder) ? "LastName_desc" : "";
            ViewData["DateSortParm"] = 
                sortOrder == "EnrollmentDate" ? "EnrollmentDate_desc" : "EnrollmentDate";

            if (searchString != null)
            {
                pageNumber = 1;
            }
            else
            {
                searchString = currentFilter;
            }

            ViewData["CurrentFilter"] = searchString;

            var students = from s in _context.Students
                           select s;
            
            if (!String.IsNullOrEmpty(searchString))
            {
                students = students.Where(s => s.LastName.Contains(searchString)
                                       || s.FirstMidName.Contains(searchString));
            }

            if (string.IsNullOrEmpty(sortOrder))
            {
                sortOrder = "LastName";
            }

            bool descending = false;
            if (sortOrder.EndsWith("_desc"))
            {
                sortOrder = sortOrder.Substring(0, sortOrder.Length - 5);
                descending = true;
            }

            if (descending)
            {
                students = students.OrderByDescending(e => EF.Property<object>(e, sortOrder));
            }
            else
            {
                students = students.OrderBy(e => EF.Property<object>(e, sortOrder));
            }
       
            int pageSize = 3;
            return View(await PaginatedList<Student>.CreateAsync(students.AsNoTracking(), 
                pageNumber ?? 1, pageSize));
        }
// </snippet_DynamicLinq>
#endif

        // GET: Students/Details/5
// <snippet_Details>
        public async Task<IActionResult> Details(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            var student = await _context.Students
                .Include(s => s.Enrollments)
                    .ThenInclude(e => e.Course)
                .AsNoTracking()
                .FirstOrDefaultAsync(m => m.ID == id);

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

            return View(student);
        }
// </snippet_Details>

        // GET: Students/Create
        public IActionResult Create()
        {
            return View();
        }

        // POST: Students/Create
// <snippet_Create>
        [HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> Create(
            [Bind("EnrollmentDate,FirstMidName,LastName")] Student student)
        {
            try
            {
                if (ModelState.IsValid)
                {
                    _context.Add(student);
                    await _context.SaveChangesAsync();
                    return RedirectToAction(nameof(Index));
                }
            }
            catch (DbUpdateException /* ex */)
            {
                //Log the error (uncomment ex variable name and write a log.
                ModelState.AddModelError("", "Unable to save changes. " +
                    "Try again, and if the problem persists " +
                    "see your system administrator.");
            }
            return View(student);
        }
// </snippet_Create>

        // GET: Students/Edit/5
        public async Task<IActionResult> Edit(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            var student = await _context.Students
                .AsNoTracking()
                .FirstOrDefaultAsync(m => m.ID == id);
            if (student == null)
            {
                return NotFound();
            }
            return View(student);
        }

        // POST: Students/Edit/5
#if (CreateAndAttach)
// <snippet_CreateAndAttach>
        public async Task<IActionResult> Edit(int id, [Bind("ID,EnrollmentDate,FirstMidName,LastName")] Student student)
        {
            if (id != student.ID)
            {
                return NotFound();
            }
            if (ModelState.IsValid)
            {
                try
                {
                    _context.Update(student);
                    await _context.SaveChangesAsync();
                    return RedirectToAction(nameof(Index));
                }
                catch (DbUpdateException /* ex */)
                {
                    //Log the error (uncomment ex variable name and write a log.)
                    ModelState.AddModelError("", "Unable to save changes. " +
                        "Try again, and if the problem persists, " +
                        "see your system administrator.");
                }
            }
            return View(student);
        }
// </snippet_CreateAndAttach>
#elif (ReadFirst)
// <snippet_ReadFirst>
        [HttpPost, ActionName("Edit")]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> EditPost(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }
            var studentToUpdate = await _context.Students.FirstOrDefaultAsync(s => s.ID == id);
            if (await TryUpdateModelAsync<Student>(
                studentToUpdate,
                "",
                s => s.FirstMidName, s => s.LastName, s => s.EnrollmentDate))
            {
                try
                {
                    await _context.SaveChangesAsync();
                    return RedirectToAction(nameof(Index));
                }
                catch (DbUpdateException /* ex */)
                {
                    //Log the error (uncomment ex variable name and write a log.)
                    ModelState.AddModelError("", "Unable to save changes. " +
                        "Try again, and if the problem persists, " +
                        "see your system administrator.");
                }
            }
            return View(studentToUpdate);
        }
// </snippet_ReadFirst>
#endif

        // GET: Students/Delete/5
// <snippet_DeleteGet>
        public async Task<IActionResult> Delete(int? id, bool? saveChangesError = false)
        {
            if (id == null)
            {
                return NotFound();
            }

            var student = await _context.Students
                .AsNoTracking()
                .FirstOrDefaultAsync(m => m.ID == id);
            if (student == null)
            {
                return NotFound();
            }

            if (saveChangesError.GetValueOrDefault())
            {
                ViewData["ErrorMessage"] =
                    "Delete failed. Try again, and if the problem persists " +
                    "see your system administrator.";
            }

            return View(student);
        }
// </snippet_DeleteGet>
        // POST: Students/Delete/5
#if (DeleteWithReadFirst)
// <snippet_DeleteWithReadFirst>
        [HttpPost, ActionName("Delete")]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> DeleteConfirmed(int id)
        {
            var student = await _context.Students.FindAsync(id);
            if (student == null)
            {
                return RedirectToAction(nameof(Index));
            }

            try
            {
                _context.Students.Remove(student);
                await _context.SaveChangesAsync();
                return RedirectToAction(nameof(Index));
            }
            catch (DbUpdateException /* ex */)
            {
                //Log the error (uncomment ex variable name and write a log.)
                return RedirectToAction(nameof(Delete), new { id = id, saveChangesError = true });
            }
        }
// </snippet_DeleteWithReadFirst>
#elif (DeleteWithoutReadFirst)
// <snippet_DeleteWithoutReadFirst>
        [HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> DeleteConfirmed(int id)
        {
            try
            {
                Student studentToDelete = new Student() { ID = id };
                _context.Entry(studentToDelete).State = EntityState.Deleted;
                await _context.SaveChangesAsync();
                return RedirectToAction(nameof(Index));
            }
            catch (DbUpdateException /* ex */)
            {
                //Log the error (uncomment ex variable name and write a log.)
                return RedirectToAction(nameof(Delete), new { id = id, saveChangesError = true });
            }
        }
// </snippet_DeleteWithoutReadFirst>
#endif
    }
}