如何在LINQ的子表上创建where条件 [英] How do I create a where condition on a sub table in LINQ
问题描述
这是对我有一个Orders集合,每个Order都有一个OrderItems集合,每个OrderItem都有一个PartId.使用LINQ如何实现以下SQL语句:
I have a collection of Orders, each Order a collection of OrderItems, and each OrderItem has a PartId. Using LINQ how do I implement the following SQL statements:
1)选择所有具有特定部件ID的订单
1) Select all the orders that have a specific part ID
SELECT *
FROM Order
WHERE Id in (SELECT OrderId FROM OrderItems WHERE PartId = 100)
2)选择Order.OrderNumber和OrderItem.PartName
2) Select the Order.OrderNumber and OrderItem.PartName
SELECT Order.OrderNumber, OrderItem.PartName
FROM Order INNER JOIN OrderItem ON Order.Id = OrderItem.OrderId
WHERE OrderItem.partId = 100
3)选择Order.OrderNumber和整个OrderItem详细信息:
3) SELECT the Order.OrderNumber and the whole OrderItem detail:
SELECT Order.OrderNumber, OrderItem.*
FROM Order INNER JOIN OrderItem ON Order.Id = OrderItem.OrderId
WHERE OrderItem.partId = 100
推荐答案
实际代码应为
1)
var orders = from o in Orders
where o.OrderItems.Any(i => i.PartId == 100)
select o;
Any()方法返回布尔值,就像SQL的"in"子句一样.这将获取所有PartItem为100的OrderItems的所有订单.
The Any() method returns a bool and is like the SQL "in" clause. This would get all the order where there are Any OrderItems what have a PartId of 100.
2a)
// This will create a new type with the 2 details required
var orderItemDetail = from o in Orders
from i in Orders.OrderItems
where i.PartId == 100
select new()
{
o.OrderNumber,
i.PartName
}
这两个from子句就像一个内部联接.
The two from clauses are like an inner join.
2b)
// This will populate the OrderItemSummary type
var orderItemDetail = from o in Orders
from i in Orders.OrderItems
where i.PartId == 100
select new OrderItemSummary()
{
OriginalOrderNumber = o.OrderNumber,
PartName = i.PartName
}
3)
// This will create a new type with two properties, one being the
// whole OrderItem object.
var orderItemDetail = from o in Orders
from i in Orders.OrderItems
where i.PartId == 100
select new()
{
OrderNumber = o.OrderNumber,
Item = i
}
由于"i"是OrderItem类型的对象,因此将Item创建为OrderItem.
Since "i" is an object of Type OrderItem, Item is create as an OrderItem.
这篇关于如何在LINQ的子表上创建where条件的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!