订单在实体框架查询中无法工作 [英] Ordering not working in Entity Framework query

问题描述

我目前正在使用实体框架（6.1.3）对我的应用程序进行一个linq查询。

I'm currently battling a linq query for my application using Entity Framework (6.1.3)

查询如下：

var productPeriods = (from pp in ctx.ProductPeriods                                          
  where pp.IsActive && pp.Product.IsBuyBackForProduct == null && !pp.Product.ProductAddOns.Any() && pp.PowerRegionID == powerRegionId
  select new
  {
      ProductPeriod = pp,
      Price = pp.Prices
        .OrderByDescending(x => x.Created)
        .GroupBy(x => x.FirmID)
        .Select(pr => pr.FirstOrDefault())
        .OrderByDescending(x => x.ProductPrice)
        .FirstOrDefault()
  }).ToList();

查询的目的是从产品期间的价格收集中查找最新价格，分组通过企业ID，然后从每个公司选择最新价格的最佳价格。

The purpose of the query is to find the latest price from the prices collection of a product period, grouped by the firm ID and then select the best price of the latest prices from each firm.

这在Linqpad中完美无缺，但第一个 OrderByDescending x => x.Created）在实体框架的上下文中使用时不起作用。

This works perfectly in Linqpad, but the first OrderByDescending(x => x.Created) doesn't work when used in context of Entity Framework.

有没有人知道为什么？也许有解决办法吗？ ： - ）

Does anyone knows why? And perhaps have a solution for it? :-)

提前感谢！

更新

感谢所有回复。我尝试了以下内容：

Thanks for all replies. I've tried the following:

select new {
    ProductPeriod = p,  
    Price = p.Prices.GroupBy(x => x.FirmID).Select(pr => pr.OrderByDescending(x => x.Created).ThenByDescending(x => x.ProductPrice).FirstOrDefault())
}

但它似乎像 ThenByDescending（x => x.ProductPrice ）也被忽略。价格在输出中没有正确排序。他们输出如下：

But it seems like ThenByDescending(x => x.ProductPrice) gets ignored as well. The prices are not sorted correctly in the output. They're output like this:

Price: 0,22940, Created: 06-03-2015 10:15:09,
Price: 0,23150, Created: 06-03-2015 10:05:48
Price: 0,20040, Created: 06-03-2015 09:24:24

更新2（现在的解决方案）

我来到解决方案，初始查询只是从每个公司返回最新的价格。目前有三家公司，所以表现应该是好的。

I came to the solution that the initial query just returns the latest prices from each firm. There's currently three firms, so the performance should be alright.

在我的代码中，在实际使用最新最优惠价格的地方，我只需要一个 .OrderByDescending（x => x.ProductPrice）.FirstOrDefault（）并检查它是否不为空。

Later in my code, where I'm actually using the latest and best price, I simply do an .OrderByDescending(x => x.ProductPrice).FirstOrDefault() and check if it's not null.

即：

var productPeriods = (from pp in ctx.ProductPeriods
                      where pp.IsActive && pp.Product.IsBuyBackForProduct == null && !pp.Product.ProductAddOns.Any() && pp.PowerRegionID == powerRegionId
                      select new
                      {
                          ProductPeriod = pp,
                          Prices = pp.Prices.GroupBy(x => x.FirmID).Select(pr => pr.OrderByDescending(x => x.Created).FirstOrDefault())
                      }).ToList();

稍后在我的代码中：

var bestPriceOfToday = period.Prices.OrderByDescending(x => x.ProductPrice).FirstOrDefault()

推荐答案

根据您的更新，omnit 选择并键入：

According to yours update, omnit select and type:

select new {
    ProductPeriod = p,  
    Price = p.Prices.GroupBy(x => x.FirmID)
        .OrderByDescending(x =>x.Created).ThenByDescending(x=>x.ProductPrice).FirstOrDefault()
}

选择是无用的，可能是问题的原因

That select was useless and could be the cause of problem

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