这是对另一个问题的答案部分中的question的回应。
我有一组订单,每个订单都是OrderItems的集合,每个OrderItem都有一个PartId。使用LINQ如何实现以下SQL语句:
1)选择具有特定零件ID的所有订单
SELECT *
FROM Order
WHERE Id in (SELECT OrderId FROM OrderItems WHERE PartId = 100)
2)选择Order.OrderNumber和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细节:
SELECT Order.OrderNumber, OrderItem.*
FROM Order INNER JOIN OrderItem ON Order.Id = OrderItem.OrderId
WHERE OrderItem.partId = 100
答案 0 :(得分:11)
实际代码应为
1)
var orders = from o in Orders
where o.OrderItems.Any(i => i.PartId == 100)
select o;
Any()方法返回一个bool,就像SQL“in”子句一样。这将得到所有订单,其中任何OrderItems的PartId为100。
2a)的
// 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子句就像一个内连接。
2b)的
// 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TypeItem类型的对象,因此Item被创建为OrderItem。