左边加入实体框架3.5

Question

I am trying to left join on entity frame work 3.5 but i am unable to do so...

from i in
    (from ta in context.test_attempt
     join uf in context.user_flag on ta.users.USERID equals uf.UserID)
select i;

I want to use left join instead to join?

Answer 1

You need to use DefaultIfEmpty() for an outer join:

from ta in context.test_attempt
join uf in context.user_flag on ta.users.USERID equals uf.UserID into g
from uf in g.DefaultIfEmpty()
select new { ta, uf }

Your outer from/select above is unnecessary, just project ta and uf into what you need.

Answer 2

Entity framework in .NET 3.5 doesn't offer left join in Linq queries. The way to get "joined records" is through navigation property between entities

From here: Left Outer Join in Entity Data Model asp.net

Answer 3

您可以在这里找到不同LINQ连接的示例： http ： //code.msdn.microsoft.com/LINQ-Join-Operators-dabef4e9以及其他LINQ示例的加载。