left join in entity framework 6.0
var query = from u in usergroups
join p in UsergroupPrices on u.UsergroupID equals p.UsergroupID into gj
from x in gj.DefaultIfEmpty()
select new {
UsergroupID = u.UsergroupID,
UsergroupName = u.UsergroupName,
Price = (x == null ? String.Empty : x.Price)
};