LINQ to Entites: sub-objects disappearing - asp.net-mvc

Question

I'm trying to understand why, sometimes, my sub-objects disappear.
In my List view, I have the standard
<% foreach (var item in Model)
and when I inspect the item and the model, I can see that item.Map has a couple of elements.
In fact, in my List view I can do:
<% foreach (var map in item.Map)
<% Html.RenderPartial("MapView", map); %>
and MapView can access and display all the properties. I'm including the sub-objects with:
list = from item in _entities.DataTable
.Include("LookupTable1")
.Include("Map")
.Include("Map.LookupTable2") select item;
return View("List", list);
But if I try to do:
<%= Html.Encode(item.Map.FirstOrDefault().Field)%>
I get a null pointer exception, and item.Map has 0 elements.
Can anyone explain why this is happening?

Answer 1

You could probably do without the .Include statements. I'm not sure if that solves your problem though, without knowing the cause of the null-pointer.
Just as a note: when doing MVC, you probably shouldn't be doing Linq queries in the view (like .FirstOrDefault).
list = from item in _entities.DataTable
select new
{
Name = item.Name
Maps = item.Maps
};
Using this syntax you can execute more Linq queries in the controller instead
list = from item in _entities.DataTable
select new
{
Name = item.Name
FirstMap = item.Maps.FirstOrDefault()
};
Or even
list = from item in _entities.DataTable
select new
{
Name = item.Name
Maps = from map in item.Maps
where map = somecondition
select map
};