Question

I want to select some fields from a datarow doing something like:

var result = datatable.AsEnumerable()
    .Select(x => new { x.Field<string>("Field1"), x.Field<string>("Field2")});

Unfortunately this isn’t working saying:

Invalid anonymous type member declarator. Anonymous type members must be declared with a member assignment, simple name or member access.

How can I achieve what I want?

Edit: As it seems there are (at least) two ways to achieve it:

1. Name ’em:

   var result = datatable.AsEnumerable().Select(x => new 
   { 
       Field1 = x.Field("Field1"), 
       Field2 = x.Field("Field2")
   });

2. Create a new object

Let’s say we have a class

class MyClass
{
    public string Field1 { get; set; }
    public string Field2 { get; set; }

    public MyClass(string field1, string field2)
    {
        this.Field1 = field1;
        this.Field2 = field2;
    }
}

we can do the following:

var result = datatable.AsEnumerable()
    .Select(x => new MyClass(x.Field<string>("Field1"), x.Field<string>("Field2")));

Answer 1

You need to give the members of your anonymous type some names.

var result = datatable.AsEnumerable()
    .Select(x => new { 
        Field1 = x.Field<string>("Field1"), 
        Field2 = x.Field<string>("Field2")});

If you think about it, no names would make it very difficult to refer to the properties later, you’d have to use reflection and some guess work. In any case, the names need to be defined so that the anonymous type can be created for you, behind the scenes.

---

If you prefer returning a Tuple instead of an anonymous type you can do

    var result = datatable.AsEnumerable()
    .Select(x => Tuple.Create( 
        Field1 = x.Field<string>("Field1"), 
        Field2 = x.Field<string>("Field2")));

Then you can access the members with Item1 and Item2 respectively.

However, the Tuple class is new to .Net 4.0 and your question is tagged 3.5

---

In response to your comment, you could always declare your own type

public class MyPair<TItem1, TItem2>
{
    public MyPair(TItem1 item1, TItem2 item2)
    {
        this.Item1 = item1;
        this.Item2 = item2;
    }

    public TItem1 Item1 { get; private set; }
    public TItem2 Item2 { get; private set; }
}

Which, obviously you would use like this,

var result = datatable.AsEnumerable()
    .Select(x => new MyPair( 
        Field1 = x.Field<string>("Field1"), 
        Field2 = x.Field<string>("Field2")));