NHibernate Fetch / ThenFetch for joined siblings - linq

Question

I have the following (simplified) hierarchy of entities:
RootClass
->DescriptorClass
->SomeChild->DescriptorClass
->SomeGrandChild
I would like to fetch everything in a single query, if possible.
Currently I have the following:
Session.Query<RootClass>().Where(/*some expressions here*/)
.Fetch(v => v.DescriptorClass)
.Fetch(v => v.SomeChild).ThenFetch(v => v.SomeGrandChild)
.Fetch(v => v.SomeChild).ThenFetch(v => v.DescriptorClass);
it works fine but it creates an SQL query with two joins on SomeChild. Obviously, I have to get rid of that second Fetch(v => v.SomeChild) but I cannot find how to do it.
I tried:
Session.Query<RootClass>().Where(/*some expressions here*/)
.Fetch(v => v.DescriptorClass)
.Fetch(v => v.SomeChild).ThenFetch(v => v.SomeGrandChild)
.ThenFetch(v => v.DescriptorClass); //<- wrong, tries to find DescriptorClass on SomeGranchild
and
Session.Query<RootClass>().Where(/*some expressions here*/)
.Fetch(v => v.DescriptorClass)
.Fetch(v => v.SomeChild).ThenFetch(v => v.SomeGrandChild)
.Fetch(v => v.DescriptorClass); //<- wrong, loads the same DescriptorClass of RootClass, not on SomeChild
How do I tell NHibernate to create a single join on SomeChild and then fetch SomeGrandChild and DescriptorClass of SomeChild?

Answer 1

For this type of query, switch to using the LINQ query syntax instead of lambdas as it gives you more control and typically outputs more efficient and cleaner SQL.
Take a look at the sample below and notice how I am able to reference the Customer entity multiple times by using the alias 'c'.
var customers =
(
from c in session.Query<Customer>()
from a in c.Addresses
from pn in c.PhoneNumbers
where c.Status == "Active"
&& a.City == "Dallas"
&& pn.AreaCode == "972"
select c )
.ToList();
This will result in the following SQL using NHibernate:
SELECT
customer0_.CustomerId as Customer1_135_0_,
customer0_.Status as Customer1_135_1_
FROM
Customer customer0_
INNER JOIN
CustomerAddresses customeraddr1_
ON customer0_.CustomerId=customeraddr1_.CustomerId
INNER JOIN
CustomerPhoneNumbers customerphon2_
ON customer0_.CustomerId=customerphon2_.CustomerId
WHERE
customer0_.Status='Active' /* #p0 */
AND customeraddr1_.City = 'Dallas' /* #p1 */
AND customerphon2_.AreaCode = '972' /* #p2 */;