title: EF4 Cascading Left Outer Joins Null Exception
body: <p>I have this query</p>
  
  <pre><code>Select p.Name,p.Street from person p
  left join address a on a.address_id = p.address_id
  left join Order o on o.order_id = a.order_id
  </code></pre>
  
  <p>But when i try to convert it into LINQ query,</p>
  
  <pre><code>var q = from p in Entities.Person 
          from a in Entities.Address.Where(a=&gt;a.address_id == p.address_id).DefaultIfEmpty()
          from o in Entities.Order.Where (o=&gt;o.order_id== a.order_Id).DefaultIfEmpty()
  </code></pre>
  
  <p>I am getting a Null exception since for some combination of address_ids there are no addresses and it blows up in o=>o.order_id== a.order_Id clause(since a is null).</p>
  
  <p>Please let me know how to do multiple left joins in EF 4, the correct way !</p>
  
  <p>Thanks !</p>