Linq内连接到组，然后选择组，为什么有空组?

Question

我正在尝试获取客户的列表及其各自的订单，但如果客户没有任何订单，则应将其排除在此列表之外。

var customerOrders = (from customer in customers
join order in orders on customer.CustomerId equals order.CustomerId into
orderGroup
select new
{
Customer.CustomerId,
Orders = orderGroup.ToList()
}).ToList();

在customerOrders列表中，我将获得没有订单或订单列表为空的客户。

我怎么能只得到有订单的客户?

Answer 1

使用where orderGroup.Any():

var customerOrders =
(
from customer in customers
join order in orders on customer.CustomerId equals order.CustomerId into orderGroup
where orderGroup.Any()
select new
{
customer.CustomerId,
Orders = orderGroup.ToList()
}
).ToList();

或group order by customer.CustomerId into g:

var customerOrders =
(
from customer in customers
join order in orders on customer.CustomerId equals order.CustomerId
group order by customer.CustomerId into g
select new
{
CustomerId = g.k,
Orders = g.ToList()
}
).ToList();