如何判断IQueryable是否为IOrderedQueryable？

Question

I have an IQueryable. I have not called OrderBy on it or otherwise done anything with it.

If I do:

// for some reason, isItOrdered is always true
var isItOrdered = myQueryable is IOrderedQueryable<T>

Why is this always true? (It seems like it shouldn't be.) And, more importantly, how can I tell if an IQueryable already has been ordered? (ie is truly an IOrderedQueryable)

I would like to be able to do something like:

if (myQueryable is IOrderedQueryable<T>)
  myQueryable = myQueryable.ThenBy(...);
else
  myQueryable = myQueryable.OrderBy(...);

Answer 1

You haven't shown what's creating your queryable to start with, but perhaps it's naturally ordered in some way?

What you've got does check whether it's really an IOrderedQueryable<T> - I suspect that it's just that your query provider always provides an ordered queryable, even if the order isn't obvious.

EDIT: Okay, something else you might try:

if (typeof(IOrderedQueryable<T>).IsAssignableFrom(myQueryable.Expression.Type))

... or in general, print out myQueryable.Expression.Type and see what it looks like.

Answer 2

This seems to work

if (query.Expression.Type == typeof(IOrderedQueryable<T>))
    myQueryable = myQueryable.ThenBy(...);
else
    myQueryable = myQueryable.OrderBy(...);

Answer 3

Some IQueryable implementations reuse the same class for IOrderedQueryable<T> .

There isn't much of a point in checking if it's really already ordered unless you know how it's ordered, otherwise you might order by the exact same property when you call ThenBy() .

Also, you can't call Queryable.ThenBy() on myQueryable if it's a reference to IQueryable —you have to cast it first:

if (myQueryable is IOrderedQueryable<T>)
   myQueryable = ((IOrderedQueryable<T>) myQueryable).ThenBy(...);