LINQ - The difference between .Select(n => n.Name) and .Select(n => new { n.Name } );

Question

I am completely new to Linq and wondering if you can help me understand the difference between the following Linq? For example...

//normal select
var contacts = entity.Contacts.Select(n => n.FirstName);

//select new
var contacts2 = entity.Contacts.Select(n => new { n.FirstName });

//normal select output
foreach (var c in contacts)
    Response.Write(c + "<br/>");

//select new output
foreach (var c in contacts2)
    Response.Write(c.FirstName + "<br/>");

The only difference I can see is that in the normal select, the firstname (string) is stored in the collection, whereas in the select new, a contact object is stored in the collecton and the firstname being accessed by its property. Also the select new returns the properties only selected in the statement.

Another difference I noticed is that you can return multiple specific properties in the select new.

In what scenario would you choose one over the other?

Thanks for the help.

Answer 1

n => n.FirstName gives you a string

n => new { n.FirstName } gives you an anonymous type, with one string property called FirstName

In general, an anonymous type with just one property is probably not what you're looking for, so I'd go for the first option.

Answer 2

To support Richard Ev's answer:

If you are not familiar with Anonymous types, crack up ildasm and give your exe as an input to it.

You will get something like this:

The thing that you see starting with <>f_AnonymousType() is the one that Richard Ev is talking about. Your syntax of new got translated into a new class (the name was decided by compiler). That is why var keyword is so helpful working with anonymous type.