LINQ to Entities group-by 失败使用 .date [英] LINQ to Entities group-by failure using .date

问题描述

我正在尝试根据日期时间字段的日期部分创建一个 Linq 组.

I am trying to do a Linq group by on just the date part of a datetime field.

此 linq 语句有效，但它按日期和时间分组.

This linq statement works but it groups by the date and the time.

var myQuery = from p in dbContext.Trends
          group p by p.UpdateDateTime into g
          select new { k = g.Key, ud = g.Max(p => p.Amount) };

当我运行此语句以仅按日期分组时，出现以下错误

When I run this statement to group by just the date I get the following error

var myQuery = from p in dbContext.Trends
          group p by p.UpdateDateTime.Date into g   //Added .Date on this line
          select new { k = g.Key, ud = g.Max(p => p.Amount) };

LINQ to Entities 不支持指定的类型成员日期".仅支持初始值设定项、实体成员和实体导航属性.

The specified type member 'Date' is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported.

如何根据日期而不是日期和时间进行分组?

How can I do a group by for the date and not the date and time?

推荐答案

使用 EntityFunctions.TruncateTime 方法:

var myQuery = from p in dbContext.Trends
          group p by EntityFunctions.TruncateTime(p.UpdateDateTime) into g
          select new { k = g.Key, ud = g.Max(p => p.Amount) };

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