Outer join in LINQ to SQL

LINQ to SQL provides direct access to inner joins only. However, it does take much to write an outer join either.

from l in context.LeftTable
join x in context.RightTable on l.Id equals x.LeftTableId into y
from r in y.DefaultIfEmpty()

Unfortunately I can no longer remember where I learned this from so I can’t give credit.

Joel Albahari points out in an MSDN thread that it is not necessary to use the join keyword at all and presents this, (IMO) much more understandable version:

from l in context.LeftTable
from r in context.RightTable.Where(x => x.LeftTableId == l.Id).DefaultIfEmpty()

The above snippets accomplish the same as

from LeftTable l
left join RightTable r on l.Id = r.LeftTableId

in regular SQL. The key in both solutions is the DefaultIfEmpty()