The following entity framework query returns all the ContactIDs for Contacts missing FormTypes required by their ContactType when querying against both Sql Server and Oracle.
var contactNeedsFormTypes =
from c in Contacts
from ft in c.ContactType.FormTypes
select new { ft.FormTypeID, c.ContactID};
var contactHasFormTypes =
from c in Contacts
from f in c.Forms
select new { c.ContactID, f.FormTypeID};
var contactsMissingFormTypes =
from n in contactNeedsFormTypes
join h in contactHasFormTypes
on new {n.ContactID, n.FormTypeID} equals new {h.ContactID, h.FormTypeID}
into jointable
where jointable.Count()==0
select n.ContactID;
contactsMissingFormTypes.Distinct();