LINQ到实体无​​法识别方法“System.TimeSpan减（System.DateTime的）'方法 [英] LINQ to Entities does not recognize the method 'System.TimeSpan Subtract(System.DateTime)' method

问题描述

我尝试在60天当前日期，选择在数据库中的记录30天20天型动物。

I try to select records in database in 60 days 30 days 20 days differents in current date.

请参阅此查询在下面。

 var uploads = (
                from files in _fileuploadRepository.Table
                join product in _productRepository.Table on files.Event equals product.Id
                where
                    (
                product.EventDate != null &&
                    (product.EventDate.Subtract(DateTime.Now).Days <= 60 && product.EventDate.Subtract(DateTime.Now).Days >= 60) ||
                    (product.EventDate.Subtract(DateTime.Now).Days <= 30 && product.EventDate.Subtract(DateTime.Now).Days >= 30) ||
                    (product.EventDate.Subtract(DateTime.Now).Days <= 20 && product.EventDate.Subtract(DateTime.Now).Days >= 20))
                    &&
                files.IsSkiped == false
                select files;
            ).ToList();

但出现错误此查询。

But a error occurred this query.

我无言以对。请帮助。

推荐答案

最简单的方法就是制定出界的前的执行查询语句：

The simplest approach is to work out the bounds before you perform the query:

// Only evaluate DateTime.Now once for consistency. You might want DateTime.Today instead.
DateTime now = DateTime.Now;
DateTime nowPlus60Days = now.AddDays(60);
DateTime nowPlus30Days = now.AddDays(30);
DateTime nowPlus20Days = now.AddDays(20);

var query = ...
            where product.EventDate <= nowPlus60Days
            ...

请注意，您的当前查询甚至没有什么意义，因为每个或'D子句，说明给定的计算既小于或等于价值的和的大于或等于相同的值。如果你想简单的等于，然后使用它。如果没有，目前还不清楚是什么你的是的尝试做的。

Note that your current query doesn't even really make sense, as each "or"'d clause is stating that the given computation is both less than or equal to a value and greater than or equal to the same value. If you want simple "equal to" then use that. If not, it's not clear what you are trying to do.

如果你想的价值观水桶到小于20，20-30，30-60，60多个你需要使用某种形式的分组。

If you're trying to bucket the values into "less than 20", "20-30", "30-60", "more than 60" you'll need to use grouping of some form.

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