如何在 EntityFramework 中按 DateTime.Date 分组

How to group by DateTime.Date in EntityFramework(如何在 EntityFramework 中按 DateTime.Date 分组)

问题描述

我有一个设备型号:

public class DeviceModel
{
    public DateTime Added { get;set; }
}

我想选择设备计数，按 Added 日期(不是日期和时间，而只有日期)分组.我当前的实现无效，因为 linq 无法将 DateTime.Date 转换为 sql:

And i want to select devices count, grouped by Added date (not Date and Time, but only date). My current implementation is not valid, because linq can't translate DateTime.Date to sql:

var result = (
    from device in DevicesRepository.GetAll()
    group device by new { Date = device.Added.Date } into g
    select new
        {
            Date = g.Key.Date,
            Count = g.Count()
        }
    ).OrderBy(nda => nda.Date);

如何更改此查询以使其正常工作?

How to change this query to make it work?

推荐答案

嗯，根据this MSDN 文档，Date 属性受 LINQ to SQL 支持，我假设 Entity Framework 也支持它.

Well, according to this MSDN document, Date property is supported by LINQ to SQL and I'd assume that Entity Framework supports it as well.

不管怎样，试试这个查询(注意我正在使用 TruncateTime 方法以避免重复解析日期):

Anyway, try this query (notice that I'm using TruncateTime method in order to avoid resolving the date repeatedly):

var result = from device in
                 (
                     from d in DevicesRepository.GetAll()
                     select new 
                     { 
                         Device = d, 
                         AddedDate = EntityFunctions.TruncateTime(d.Added) 
                     }
                 )
             orderby device.AddedDate
             group device by device.AddedDate into g
             select new
             {
                 Date = g.Key,
                 Count = g.Count()
             };

希望这会有所帮助.

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