LINQ INNER JOIN中的条件组合键 [英] LINQ Conditional Composite key in INNER JOIN

问题描述

假设我有一个Order和OrderDetails集合.如何用LINQ(查询或流利的语法)编写以下sql?

Let's say I have an Order and OrderDetails collections. How can I write following sql in LINQ (query or fluent syntax)?

选择前1个OD.ProductId
来自订单O
OD.OrderID = 1上的内部联接OrderDetail OD
和OD.OrderId = O.OrderId
和((OD.OrderDate = O.OrderDate)或(OD.OrderDate为空))
其中O.CustomerId = 2
通过OD.OrderDate desc排序

select top 1 OD.ProductId
from Order O
inner join OrderDetail OD on OD.OrderID = 1
and OD.OrderId = O.OrderId
and ((OD.OrderDate = O.OrderDate) or (OD.OrderDate is null))
where O.CustomerId = 2
order by OD.OrderDate desc

我知道我可以创建一个匿名类型，其中包含与联接匹配的所有列，但是如上所述，如何在 BOLD

I know that I can create an anonymous type containing all the columns to match for join however how can I write conditional logic for inner join as mentioned above in BOLD

推荐答案

您的查询将给出与以下结果相同的结果:

Your query will give the same results as:

select top 1 OD.ProductId
from Order O
inner join OrderDetail OD
  on OD.OrderId = O.OrderId
where O.CustomerId = 2
  and OD.OrderID=1
  and (OD.OrderDate is null or OD.OrderDate=O.OrderDate)
order by OD.OrderDate desc

您应该能够轻松地将其转换为LINQ.

You should be able to convert that to LINQ much easier.

var results=db.OrderDetail
  .Where(od=>od.Order.CustomerId==2)
  .Where(od=>od.OrderId==1)
  .Where(od=>od.OrderDate==null || od.OrderDate==od.Order.OrderDate)
  .OrderBy(od=>od.OrderDate)
  .Select(od=>od.ProductId)
  .First();

您可以进一步简化为:

var results=db.OrderDetail
  .Where(od=>od.Order.CustomerId==2 &&
    (od.OrderId==1) &&
    (od.OrderDate==null || od.OrderDate==od.Order.OrderDate))
  .OrderBy(od=>od.OrderDate)
  .Select(od=>od.ProductId)
  .First();

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