一个数据库中的几个汇总操作往返 [英] Several summary operations in one database roundtrip

问题描述

使用总摘要的Linq查询的大多数示例是一个返回单个聚合操作的查询。

如何进行多次汇总操作，导致只有一次往返数据库。

例如，我想计算orderdetails的数量（使用某些条件），并且还要计算行数的总和。

Soemthing就像一个SQL查询：

从Orderdetails中选择count（*），sum（price * amount）...

不是我想要做的事情，我想要的比这个例子复杂一点，但只是想知道我需要做什么。要获得这些摘要很简单，但想知道如何通过一次往返数据库来实现它。

Most examples of Linq queries using total summaries is one query returning a single aggregated operation.

How can you have several  summary operations resulting in only one roundtrip to database.

For example I want to count the number of orderdetails (using some conditions) and also make a sum of the amount of row.

Soemthing like an SQL query:

Select count(*), sum(price*amount) from Orderdetails where ...

Not really what I am trying to do, what I want is a bit more complex than this example, but just to get some idea what I need to do. To get those summaries is easy but want to know how I can do it with just one roundtrip to database.

推荐答案

你尝试过这样的事吗？< br>
来自o的context.Orders选择
new {
o.Id
OrderPrice = o.OrderDetails.Sum（od => od.Price * od.Amount），
OrderDetailsCount = o.OrderDetails.Count（）
}

Have you tried something like this?

from o in context.Orders select
new {
    o.Id
    OrderPrice = o.OrderDetails.Sum(od => od.Price * od.Amount),
    OrderDetailsCount = o.OrderDetails.Count()
}

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