Question

Why is it it gives error in return View(contacts.ToPagedList(pageNumber, pageSize)); statement the error in the Index method :
The method 'Skip' is only supported for sorted input in LINQ to Entities. The method 'OrderBy' must be called before the method 'Skip'.

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.Entity;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using PhoneBook.Models;
using PagedList;

namespace PhoneBook.Controllers
{ 
public class ContactsController : Controller
{
    private PhoneDBContext db = new PhoneDBContext();

    //
    // GET: /Contacts/

    public ViewResult Index(string searchString, string sortOrder, Contact model, string currentFilter, int? page)
    {
        ViewBag.CurrentSort = sortOrder;

        ViewBag.FNameSortParm = sortOrder == "FName asc"? "FName desc" : "FName asc";
        ViewBag.DateSortParm = sortOrder == "Date asc" ? "Date desc" : "Date asc";
        ViewBag.LNameSortParm = sortOrder == "LName asc" ? "LName desc" : "LName asc";
        ViewBag.CompSortParm = sortOrder == "Company asc" ? "Company desc" : "Company asc";
        ViewBag.MobSortParm = sortOrder == "Mob asc" ? "Mob desc" : "Mob asc";
        ViewBag.TelSortParm = sortOrder == "Tel asc" ? "Tel desc" : "Tel asc";

        if (Request.HttpMethod == "GET") { searchString = currentFilter; }
        else {page = 1;}
        ViewBag.CurrentFilter = searchString;
        var contacts = from m in db.Contacts
                       select m;

        switch (sortOrder)
        {
            case "FName desc":
                contacts = contacts.OrderByDescending(s => s.FirstName);
                break;
            case "FName asc":
                contacts = contacts.OrderBy(s => s.FirstName);
                break;
            case "LName desc":
                contacts = contacts.OrderByDescending(s => s.LastName);
                break;
            case "LName asc":
                contacts = contacts.OrderBy(s => s.LastName);
                break;
            case "Company desc":
                contacts = contacts.OrderByDescending(s => s.Company);
                break;
            case "Company asc":
                contacts = contacts.OrderBy(s => s.Company);
                break;
            case "Date desc":
                contacts = contacts.OrderByDescending(s => s.DateAdded);
                break;
            case "Date asc":
                contacts = contacts.OrderBy(s => s.DateAdded);
                break;
            case "Mob desc":
                contacts = contacts.OrderByDescending(s => s.MobileNumber);
                break;
            case "Mob asc":
                contacts = contacts.OrderBy(s => s.MobileNumber);
                break;
            case "Tel desc":
                contacts = contacts.OrderByDescending(s => s.TelephoneNumber);
                break;
            case "Tel asc":
                contacts = contacts.OrderBy(s => s.TelephoneNumber);
                break;
        }


        if (!String.IsNullOrEmpty(searchString))
        {
            contacts = contacts.Where(s => s.LastName.ToUpper().Contains(searchString)||s.FirstName.ToUpper().Contains(searchString)||s.Company.ToUpper().Contains(searchString));
        }

        int pageSize = 3;
        int pageNumber = (page ?? 1);

       return View(contacts.ToPagedList(pageNumber, pageSize));
    }

    //
    // GET: /Contacts/Details/5

    public ViewResult Details(int id)
    {
        Contact contact = db.Contacts.Find(id);
        return View(contact);
    }

    //
    // GET: /Contacts/Create

    public ActionResult Create()
    {
        return View();
    } 

    //
    // POST: /Contacts/Create

    [HttpPost]
    public ActionResult Create(Contact contact)
    {
        if (ModelState.IsValid)
        {
            db.Contacts.Add(contact);
            contact.DateAdded = DateTime.Now;
            db.SaveChanges();
            return RedirectToAction("Index");  
        }

        return View(contact);
    }

    //
    // GET: /Contacts/Edit/5

    public ActionResult Edit(int id=0)
    {

        Contact contact = db.Contacts.Find(id);

        if (contact == null)    { return HttpNotFound(); } // returns blank page if id is not valid
        return View(contact);
    }

    //
    // POST: /Contacts/Edit/5

    [HttpPost]
    public ActionResult Edit(Contact contact)
    {
        if (ModelState.IsValid)
        {


            db.Entry(contact).State = EntityState.Modified;
            contact.DateAdded = DateTime.Now;
            db.SaveChanges();
            return RedirectToAction("Index");
        }
        return View(contact);
    }

    //
    // GET: /Contacts/Delete/5

    public ActionResult Delete(int id)
    {
        Contact contact = db.Contacts.Find(id);
        if (contact == null) { return HttpNotFound(); }
        return View(contact);
    }

    //
    // POST: /Contacts/Delete/5

    [HttpPost, ActionName("Delete")]
    public ActionResult DeleteConfirmed(int id)
    {            
        Contact contact = db.Contacts.Find(id);
        if (contact == null) { return HttpNotFound(); }
        db.Contacts.Remove(contact);
        db.SaveChanges();
        return RedirectToAction("Index");
    }

    public ActionResult SearchIndex(string searchString)
    {
        var contacts = from m in db.Contacts
                     select m;

        if (!String.IsNullOrEmpty(searchString))
        {
            contacts = contacts.Where(s => s.LastName.Contains(searchString));
        }

        return View(contacts);
    }

    protected override void Dispose(bool disposing)
    {
        db.Dispose();
        base.Dispose(disposing);
    }


}
}

below is the Index.cshtml code:

@model PagedList.IPagedList<PhoneBook.Models.Contact>
@{
    ViewBag.Title = "Phone Book";
}

<p>

     @using (Html.BeginForm()){   
         <p> Search: @Html.TextBox("SearchString", ViewBag.CurrentFilter as string) 
         <input type="submit" value="Go" /></p>
        }
</p>


<p>
    @Html.ActionLink("Create New", "Create")
</p>

<table>
    <tr>
        <th>
             @Html.ActionLink("First Name", "Index", new { sortOrder=ViewBag.FNameSortParm, currentFilter=ViewBag.CurrentFilter })
        </th>
        <th>
             @Html.ActionLink("Last Name", "Index", new { sortOrder = ViewBag.LNameSortParm, currentFilter = ViewBag.CurrentFilter })
        </th>
        <th>
            @Html.ActionLink("Mobile Num", "Index", new { sortOrder = ViewBag.MobSortParm, currentFilter = ViewBag.CurrentFilter })
        </th>
        <th>
            @Html.ActionLink("Tel Num", "Index", new { sortOrder = ViewBag.TelSortParm, currentFilter = ViewBag.CurrentFilter })
        </th>
        <th>
             @Html.ActionLink("Company", "Index", new { sortOrder = ViewBag.CompSortParm, currentFilter = ViewBag.CurrentFilter })
        </th>
        <th>
           @Html.ActionLink("Date Added/Updated", "Index", new { sortOrder = ViewBag.DateSortParm, currentFilter = ViewBag.CurrentFilter })
        </th>
        <th></th>
    </tr>

@foreach (var item in Model) {
    <tr>
        <td>
            @Html.DisplayFor(modelItem => item.FirstName)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.LastName)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.MobileNumber)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.TelephoneNumber)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.Company)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.DateAdded)
        </td>
        <td>
            @Html.ActionLink("Details", "Details", new { id=item.ID })
            @Html.ActionLink("Edit", "Edit", new { id=item.ID }) 
            @Html.ActionLink("Delete", "Delete", new { id=item.ID })
        </td>
    </tr>
}

</table>

<div>
    Page @(Model.PageCount < Model.PageNumber ? 0 : Model.PageNumber)
    of @Model.PageCount

    @if (Model.HasPreviousPage)
    {
        @Html.ActionLink("<<", "Index", new { page = 1, sortOrder = ViewBag.CurrentSort, currentFilter=ViewBag.CurrentFilter  })
        @Html.Raw(" ");
        @Html.ActionLink("< Prev", "Index", new { page = Model.PageNumber - 1, sortOrder = ViewBag.CurrentSort, currentFilter=ViewBag.CurrentFilter  })
    }
    else
    {
        @:<<
        @Html.Raw(" ");
        @:< Prev
    }

    @if (Model.HasNextPage)
    {
        @Html.ActionLink("Next >", "Index", new { page = Model.PageNumber + 1, sortOrder = ViewBag.CurrentSort, currentFilter=ViewBag.CurrentFilter  })
        @Html.Raw(" ");
        @Html.ActionLink(">>", "Index", new { page = Model.PageCount, sortOrder = ViewBag.CurrentSort, currentFilter=ViewBag.CurrentFilter  })
    }
    else
    {
        @:Next >
        @Html.Raw(" ")
        @:>>
    }
</div>

Answer 1

Try the following three changes.

1. Put this code before the switch statement:

   if (!String.IsNullOrEmpty(searchString))
   {
       contacts = contacts.Where(s => s.LastName.ToUpper().Contains(searchString)||s.FirstName.ToUpper().Contains(searchString)||s.Company.ToUpper().Contains(searchString));
   }
   

2. Add a default case in your switch statement, and make it throw.

   switch (sortOrder) {
       case ...:
           ...
       default:
           throw new ArgumentException("Bad sort order specified", "sortOrder");
   }
   

3. Use the type IOrderedQueryable<T>.

   IOrderedQueryable<T> orderedContacts;
   switch (sortOrder)
   {
       case "FName desc":
           orderedContacts = contacts.OrderByDescending(s => s.FirstName);
           break;
       ...
   }
   
   ...
   
   return View(orderedContacts.ToPagedList(pageNumber, pageSize));