Linq query with multiple Sums, Groupings and Joins

I have an SQL query which I need to translate to Linq to SQL. I was successful until it came to Sums and I'm completely stuck there. I know how to do single/simple groupings and sums but this time I desperately need help. I'd appreciate any ideas.

Table relations are like this:

TreeNodes - one-to-many - Dispatches (not every TreeNode has Dispatch entry)
Dispatches - one-to-many - DispatchesJobs (not every Dispatch has DispatchJob entry)
DispatchesJobs one-to-many - DispatchesJobsReceivings (not every DispatchJob has DispatchJobReceiving entry)

Basically what I need to find out is:

For every Dispatch: Get the Dispatch's TreeNode name and its quantity, spent, return count from the DispatchesJobsReceivings table.

Here's my SQL query:

select t.TreeNodes_id, t.name
sum(djr.quantity) as quantity, sum(djr.returns) as returns, sum(djr.spent) as spent

from TreeNodes as t

inner join Dispatches as d
on t.TreeNodes_id = d.TreeNodes_id

left outer join DispatchesJobs as dj
on d.Dispatches_id = dj.Dispatches_id

left outer join DispatchesJobsReceivings as djr
on dj.DispatchesJobs_id = djr.DispatchesJobs_id

group by t.TreeNodes_id, t.name

Which gives this result:

TreeNodes_id name      quantity  returns  spent
------------ ------------ -------   -------  ---------- 
77        CEMENT      20     17      3
122       SAND           NULL    NULL     NULL

I've come this far translating it:

from t in db.TreeNodes

join d in db.Dispatches
on t.TreeNodes_id equals d.TreeNodes_id

join dj in db.Dispatches_Jobs
on d.Dispatches_id equals dj.Dispatches_id
into tmpDJ
from rowTmpDJ in tmpDJ.DefaultIfEmpty()

join djr in db.DispatchesJobsReceivings
on rowTmpDj.DispatchesJobs_id equals djr.DispatchesJobs_id
into tmpDjr
from rowTmpDjr in tmpDjr.DefaultIfEmpty()

select new 
{
   TreeNode_id = t.TreeNodes_id,
   name = t.name,
   quantity = rowTmpDjr.quantity,
   returns = rowTmpDjr.returns,
   spent = rowTmpDjr.spent
};

Which gives this result:

 TreeNodes_id name      quantity  returns  spent
 ------------ ------------ ------    -------- ----------
 77           CEMENT          1         0         1
 77           CEMENT          2         0         2
 77   开发者_运维知识库        CEMENT          4         4         0
 77           CEMENT          13     13        0
 122          SAND            NULL      NULL      NULL

And I'm stuck right here. I'd appreciate any help.

---

Look at a product named Linqer (I have no association with it). It converts T-SQL to LINQ queries. Fantastic tool. I have to run across a query it hasn't been able to convert. There is a 30 day trial with it. Cost is around $60.

Randy