C# - AsEnumerable Example

Question

What is the exact use of AsEnumerable? Will it change non-enumerable collection to enumerable collection?.Please give me a simple example.

Answer 1

Here's example code which may illustrate LukeH's correct explanation.

IEnumerable orderQuery = dataContext.Orders
  .Where(o => o.Customer.Name == "Bob")
  .AsEnumerable()
  .Where(o => MyFancyFilterMethod(o, MyFancyObject));

The first Where is Queryable.Where, which is translated into sql and run in the database (o.Customer is not loaded into memory).

The second Where is Enumerable.Where, which calls an in-memory method with an instance of something I don't want to send into the database.

Without the AsEnumerable method, I'd have to write it like this:

IEnumerable orderQuery =
  ((IEnumerable)
    (dataContext.Orders.Where(o => o.Customer.Name == "Bob")))
  .Where(o => MyFancyFilterMethod(o, MyFancyObject));

Or

IEnumerable orderQuery =
  Enumerable.Where(
    dataContext.Orders.Where(o => o.Customer.Name == "Bob"),
    (o => MyFancyFilterMethod(o, MyFancyObject));

Neither of which flow well at all.