c# - LEFT OUTER JOIN in LINQ -

how perform left outer join in c# linq objects without using join-on-equals-into clauses? there way where clause? correct problem: inner join easy , have solution this

list<joinpair> innerfinal = (from l in lefts r in rights l.key == r.key                              select new joinpair { leftid = l.id, rightid = r.id}) 

but left outer join need solution. mine it's not working

list< joinpair> leftfinal = (from l in lefts r in rights                              select new joinpair {                                              leftid = l.id,                                              rightid = ((l.key==r.key) ? r.id : 0                                         }) 

where joinpair class:

public class joinpair { long leftid; long rightid; } 

as stated on:

101 linq samples - left outer join

var q =     c in categories     join p in products on c.category equals p.category ps     p in ps.defaultifempty()     select new { category = c, productname = p == null ? "(no products)" : p.productname };