分类:
EF
linq ( DefaultIfEmpty()方法是核心方法，添加此方法在后台才能产生 lift join的SQL语句，不添加则为join)
//使用linq
var database = from c in oaentities.Userchild
join f in oaentities.Userfather on c.Fid equals f.Cid into leftjointemp
from leftjoin in leftjointemp.DefaultIfEmpty()
select new
{
c.sid,
c.Username,
leftjoin.Fathername
};
var joinfdatabase = database.ToList();lamdba表达式（使用GroupJoin ，GroupJoin是一对多的方法，SelectMany是一对一的方法）
var database = oaentities.Userchild.GroupJoin(oaentities.Userfather, a => a.Fid, b => b.Cid, (user, parent) => new
{
//主表字段可以点出来
user = user,
//附表字段不能点出来
Father = parent
}).SelectMany(a => a.Father.DefaultIfEmpty(), (last, parent) => new LeftJoinDatabeseController {
//给需要显示的字段赋值（LeftJoinDatabeseController 类需要自己创建，需要显示的字段是这个类的成员）
sid = last.user.sid,
Username = last.user.Username,
Fathername = parent.Fathername
});
//向前台输出
ViewBag.joinfdatabase = database.ToList();评价
