Question

我有一个设备型号：

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

我想选择设备数量，按Added日期分组（不是日期和时间，但只有日期）。我当前的实现无效，因为linq无法将DateTime.Date转换为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？

Answer 1

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

无论如何，请尝试此查询（请注意我正在使用TruncateTime方法以避免重复解析日期）：

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。

Answer 2

使用EntityFunctions.TruncateTime

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

如何在EntityFramework中按DateTime.Date进行分组

2 个答案: