from t1 in table1
join t2 in table2 on t1.Id equals t2.Id into t2g
from t2 in t2g.DefaultIfEmpty()
join t3 in table3 on t2.Id equals t3.Id into t3g
from t3 in t3g.DefaultIfEmpty()
join t4 in table4 on t3.Id equals t4.Id into t4g
from t4 in t4g.DefaultIfEmpty()
selectnew { t1, t2, t3, t4 }


linq to entity 的多表外连语句