Enumeration Succeeds after DbContext Disposed - entity-framework

Question

Background
I am creating a projection from a parent/child relationship that includes a Name property of the parent and a list of the children's Ids.
Code
private class ParentChildInfo
{
public string Name { get; set; }
public List<int> ChildIds { get; set; }
}
var infos = ctx.Masters.Include(m => m.Children).Select(
m => new ParentChildInfo()
{
Name = m.Name,
ChildIds = m.Children.Where(c => c.SomeProp.StartsWith("SpecialValue"))
.Select(c => c.Id).ToList()
}).ToList();
Unfortunately that produced the error
LINQ to Entities does not recognize the method 'System.Collections.Generic.List`1[System.Int32] ToList[Int32]
That lead me to this post, which suggested (in the comments) making the following changes:
private class ParentChildInfo
{
public string Name { get; set; }
public IEnumerable<int> ChildIds { get; set; } // No longer List<int>
}
var infos = ctx.Masters.Include(m => m.Children).Select(
m => new ParentChildInfo()
{
Name = m.Name,
ChildIds = m.Children.Where(c => c.SomeProp.StartsWith("SpecialValue"))
.Select(c => c.Id) // Dropped the .ToList()
}).ToList();
I originally wanted to get lists rather than enumerables because the code that uses the result runs for several minutes, and I did not want to tie up the DbContext that long.
I use the code like this:
using (MyContext ctx = new MyContext())
{
// code from above that populates infoes
}
foreach (var info in infoes)
{
// use info.ChildIds
}
I planned to move the foreach into the using so that I can enumerate the ChildIds, but hit F5 instead and was surprised to see that the code works.
Question
Given that the DbContext is disposed at that point and ChildIds is an IEnumerable<int> rather than List<int>, why exactly can I enumerate ChildIds?

Answer 1

It is because the ToList() of the infos query actually executes the query. So the collection ctx.Masters is enumerated and the projections are populated. Even without the Include it would notice that Master.Children is addressed and emit the SQL join. The implementing type of IEnumerable<int> ChildIds is probably List<int>.

Answer 2

You did .ToList() on the query so the query was executed and all the results are materialized and the connection to the database should be closed. I assume it would not work if you did not have .ToList() since (at least in EF5) the results are being processed in streaming fashion and entities are materialized when requested (i.e. on each iteration in the loop).