如何获取Linq查询的outerjoin

要获取外部联接,可以使用DefaultIfEmpty。请看这个问题: Linq to Sql: Multiple left outer joins

from c in context.Customers
from o in context.Orders
    .Where(a => a.customerid == c.id)
    .DefaultIfEmpty()
where c.City == "MyCity" || o.ShipTo == "MyCity"
select c

或者,您可以执行以下操作:

from c in context.Customers
join o in context.Orders on c.id equals o.customerid into g
from x in g.DefaultIfEmpty() 
where c.City == "MyCity" || x.ShipTo == "MyCity"
select c

我相信它们都生成相同的SQL。

你必须使用 DefaultIfEmpty

var result = from c in context.Customers
    join o in c.Orders on c.CustomerId equals o.CustomerId into lj
    from or in lj.DefaultIfEmpty()
    where c.City == "MyCity" || or.ShipTo == "MyCity"
    select c