How to use LINQ Contains() to find a list of enums?

Question

I have an enum called OrderStatus, and it contains various statuses that an Order can be in:

• Created
• Pending
• Waiting
• Valid
• Active
• Processed
• Completed

What I want to do is create a LINQ statement that will tell me if the OrderStaus is Valid, Active, Processed or Completed.

Right now I have something like:

var status in Order.Status.WHERE(status => 
      status.OrderStatus == OrderStatus.Valid || 
      status.OrderStatus == OrderStatus.Active|| 
      status.OrderStatus == OrderStatus.Processed|| 
      status.OrderStatus == OrderStatus.Completed)

That works, but it's very "wordy". Is there a way to convert this to a Contains() statement and shorten it up a bit?

Answer 1

Sure:

var status in Order.Status.Where(status => new [] {
        OrderStatus.Valid, 
        OrderStatus.Active, 
        OrderStatus.Processed,
        OrderStatus.Completed
    }.Contains(status.OrderStatus));

You could also define an extension method In() that would accept an object and a params array, and basically wraps the Contains function:

public static bool In<T>(this T theObject, params T[] collection)
{
    return collection.Contains(theObject);
}

This allows you to specify the condition in a more SQL-ish way:

var status in Order.Status.Where(status => 
    status.OrderCode.In(
        OrderStatus.Valid, 
        OrderStatus.Active, 
        OrderStatus.Processed,
        OrderStatus.Completed));

Understand that not all Linq providers like custom extension methods in their lambdas. NHibernate, for instance, won't correctly translate the In() function without additional coding to extend the expression parser, but Contains() works just fine. For Linq 2 Objects, no problems.

Answer 2

I have used this extension:

    public static bool IsIn<T>(this T value, params T[] list)
    {

                     return list.Contains(value);           
    }

You may use this as the condition:

   Where(x => x.IsIn(OrderStatus.Valid, ... )