EF left join



Left Join 查询

from d in Doctors
join c in (
(from t in Commentaries where t.State != 'D' group t by new { t.DoctorID } into g 
select new {
DoctorID = (Int64?)g.Key.DoctorID,
Total = (Int32?)g.Sum(p => p.Rating),
Evaluate = (System.Double?)g.Average(p => p.Rating)
})) on new { UserID = d.UserID } equals new { UserID = (Int64)c.DoctorID }into a_join
from p in a_join.DefaultIfEmpty()
select new {
  d.ID,
  UserID = (Int64?)d.UserID,
  d.Name,
  Evaluate = ((int?)p.Evaluate ?? (int?)0)
}