Linq 左连接 left join

 

Suppose you have a tblRoom and tblUserInfo. Now, you need to select all the rooms regardless of whether the room has user information or not. This calls for a LEFT JOIN which will select everything from the LEFT side (the room side) regardless of the join on the right side. Here is the example.

假如你有两张表tblRoom（房 间表）和tblUserInfo（住户表）。

现在你需要检索出所有房间的信息，而不管这个房间是否有人居住。这就需要进行LEFT JOIN（左外连接），左外连接会检索出LEFT JOIN左边表中的所有行，而不管右边的表是否有匹配项。下面是一个例子：　　

 

var list = from r in dc.tblRooms
                          join ui in dc.tblUserInfos
                          on r.UserName equals ui.UserNameinto userrooms

                          from ur in userrooms.DefaultIfEmpty()

                          select new
                           {
                               FirstName = (ur.FirstName == null) ? "N/A" : ur.FirstName,
                               LastName = (ur.LastName == null) ? "N/A" : ur.LastName,
                               RoomName = r.Name
                           };

View Code