'IQueryable' does not contain a definition for 'OrderByDescending'

Question

Getting this error for the orderby in where clause. I did this because previously, if I didn't define 'people' I'd get an error on the return for people saying the name 'people' doesnt exist in this current context. How do I fix this?

 public JsonResult PersonsList(string birthyear)
 {
     TutorialDBContext db = new TutorialDBContext();
     var NumericYear = Convert.ToInt32(birthyear);
     IQueryable people;

     if (birthyear == "All")
     {
          people = from m in db.persons
                   select m;

          people = people.OrderByDescending(s => s.birthdate);
     }
     else
     {
          people = from m in db.persons
                   where m.birthdate.Year >= NumericYear
                   where m.birthdate.Year <= (NumericYear + 9)
                   select m;
     }

     return Json(people, JsonRequestBehavior.AllowGet);
 }

Answer 1

Because there is indeed no such method. There is one on that accepts an IQueryable<T> though. Use

IQueryable<Person> people;

or whatever element type would be appropriate.

Answer 2

OrderByDescending() is an extension method of IQueryable<T>, not of the non-generic IQueryable.

So you need to declare people as IQueryable<Person>.

Answer 3

As mentioned several times you'd need to declare people as an IQueryable<Person> or whatever the type returned from the People table is. If you want to use implicit typing you could rearrange your code as so:

var people = from m in db.persons
             select m;
if (birthyear == "All")
{
    people = people.OrderByDescending(s => s.birthdate);
}
else
{
     people = people.Where(p => p.birthdate.Year >= NumericYear
                             && p.birthdate.Year <= NumericYear + 9)
}

Answer 4

1. You must have using System.Linq; at the begining of the code file.
2. You should change IQueryable people; to IQueryable<Person> people;
3. If you call this method with All as birthyear value you will get an exception when you reach var NumericYear = Convert.ToInt32(birthyear);

4. I suggest to change the whole function to this

   public JsonResult PersonsList(string birthyear)
   {
       using (var db = new TutorialDBContext())
       {
           IQueryable<Person> people;
   
           if (birthyear == "All")
           {
               people = db.persons.OrderByDescending(s => s.birthdate);
           }
           else
           {
               var NumericYear = Convert.ToInt32(birthyear);
               people = from m in db.persons
                   where m.birthdate.Year >= NumericYear
                   where m.birthdate.Year <= (NumericYear + 9)
                   select m;
           }
   
           return Json(people, JsonRequestBehavior.AllowGet);
       }
   }