LINQ Get Count of 2nd level detail table

I'm trying to get the count of records from a detail table, and it's detail table in LINQ and I'm hitting a road block.

Lets say I have 3 tables in this structure:

Header
    Detail
        Items

I would like to see all Header items with the count of Detail and the count of it's Ite开发者_JAVA技巧ms.

from h in Header select new {
  h.Name,
  h.IsEnabled,
  DetailCount = h.Details.Count(),
  ItemCount = h.Details.Items.Count() <---- Here's the problem
}

You can use SelectMany:

from h in Header select new {
  h.Name,
  h.IsEnabled,
  DetailCount = h.Details.Count(),
  ItemCount = h.Details.SelectMany(d => d.Items).Count()
}

Or if you prefer you could sum the items count of each detail:

from h in Header select new {
  h.Name,
  h.IsEnabled,
  DetailCount = h.Details.Count(),
  ItemCount = h.Details.Sum(d => d.Items.Count())
}