Is this what you need?
var result = from itemA in TableA
join itemB in TableB on itemA.ID equals itemB.ID
select new { itemA, itemB };
Alternately, you could declare a result class that helps you build the result object without specifying all the fields:
class ItemAB
{
public ItemAB(ItemA a, ItemB b)
{
FieldA1 = a.FieldA1;
FieldA2 = a.FieldA2;
FieldB1 = b.FieldB1;
FieldB2 = b.FieldB2;
}
public int FieldA1 { get; private set; }
public int FieldA2 { get; private set; }
public int FieldB1 { get; private set; }
public int FieldB2 { get; private set; }
}
var result = from itemA in TableA
join itemB in TableB on itemA.ID equals itemB.ID
select new ItemAB(itemA, itemB);