C# Linq 子选择
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/527819/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Linq Sub-Select
提问by Dan
How do I write a sub-select in LINQ.
如何在 LINQ 中编写子选择。
If I have a list of customers and a list of orders I want all the customers that have no orders.
如果我有一个客户列表和一个订单列表，我想要所有没有订单的客户。
This is my pseudo code attempt:
这是我的伪代码尝试：
var res = from c in customers
where c.CustomerID ! in (from o in orders select o.CustomerID)
select c
采纳答案by Jon Skeet
How about:
怎么样：
var res = from c in customers
where !orders.Select(o => o.CustomerID).Contains(c.CustomerID)
select c;
Another option is to use:
另一种选择是使用：
var res = from c in customers
join o in orders
on c.CustomerID equals o.customerID
into customerOrders
where customerOrders.Count() == 0
select c;
Are you using LINQ to SQL or something else, btw? Different flavours may have different "best" ways of doing it
你是使用 LINQ to SQL 还是其他什么东西，顺便说一句？不同的口味可能有不同的“最佳”方式
回答by Marc Gravell
If this is database-backed, try using navigation properties (if you have them defined):
如果这是数据库支持的，请尝试使用导航属性（如果您定义了它们）：
var res = from c in customers
where !c.Orders.Any()
select c;
On Northwind, this generates the TSQL:
在 Northwind 上，这会生成 TSQL：
SELECT /* columns snipped */
FROM [dbo].[Customers] AS [t0]
WHERE NOT (EXISTS(
SELECT NULL AS [EMPTY]
FROM [dbo].[Orders] AS [t1]
WHERE [t1].[CustomerID] = [t0].[CustomerID]
))
Which does the job quite well.
这可以很好地完成工作。
回答by omoto
var res = (from c in orders where c.CustomerID == null
select c.Customers).ToList();
or Make Except()
或 Make except()
回答by amit
var result = (from planinfo in db.mst_pointplan_info
join entityType in db.mst_entity_type
on planinfo.entityId equals entityType.id
where planinfo.entityId == entityId
&& planinfo.is_deleted != true
&& planinfo.system_id == systemId
&& entityType.enity_enum_id == entityId
group planinfo by planinfo.package_id into gplan
select new PackagePointRangeConfigurationResult
{
Result = (from planinfo in gplan
select new PackagePointRangeResult
{
PackageId = planinfo.package_id,
PointPlanInfo = (from pointPlanInfo in gplan
select new PointPlanInfo
{
StartRange = planinfo.start_range,
EndRange = planinfo.end_range,
IsDiscountAndChargeInPer = planinfo.is_discount_and_charge_in_per,
Discount = planinfo.discount,
ServiceCharge = planinfo.servicecharge,
AtonMerchantShare = planinfo.aton_merchant_share,
CommunityShare = planinfo.community_share
}).ToList()
}).ToList()
}).FirstOrDefault();
