Question

How can the following be achieved with only 1 Linq query? Is it more efficient?

var o = new myObject {
    Value =
        (from value in g
        select value.Value).FirstOrDefault(),
    Id =
        (from value in g 
        select value.Id).FirstOrDefault(),
    ... }

Answer 1

var result = (from value in g 
             select new 
               {
              Value = value.Value,
              ID = value.ID
               }).FirstOrDefault();

EDIT: (Based on Edited question)
In that case I would rather have the value first and then use that in the constructor for my object. Your select may involve a condition or where clause. I think in Linq to object, performance is not going to matter that much, or may be it depends on the collection size, but I still believe it will be minimal. Still the best approach would be to select the item first and then use it in object initialization.

var result = (from value in g 
             select new 
               {
              Value = value.Value,
              ID = value.ID
               }).FirstOrDefault();

var o = new myObject{Value = result.Value, ID = result.ID}