实体框架按日期分组并返回新类

Question

我正在使用.NET和实体框架.我希望按照没有时间部分的日期对表进行分组.

我上课了:

public sealed class QueryItem {
    public int Year { get; set; }
    public int Month { get; set; }
    public int Day { get; set; }
}

和方法(我正在使用BLToolkit,如果你想知道什么是DbManager):

protected override IQueryable<QueryItem> InitiateQuery() {
    return
        from query in DbManager.GetTable<SomeTableModel>()
        group query by new { Year = query.CreationDate.Year, Month = query.CreationDate.Month, Day = query.CreationDate.Day }
        into list1
        select new QueryItem {Year = list1.Key.Year, Month = list1.Key.Month, Day = list1.Key.Day};
}

在这个方法中,linq翻译成了这个SQL查询:

SELECT
    [query].[CreationDate]
FROM
    [SomeDatabase.SomeTable] [query]
GROUP BY
    DatePart(Year, [query].[CreationDate]),
    DatePart(Month, [query].[CreationDate]),
    DatePart(Day, [query].[CreationDate]),
    [query].[CreationDate]

这是错误的查询,因为它不仅仅按日期分组.

但是如果我使用这段代码(它不可用,我需要返回一个类对象):

var result =
    from query in DbManager.GetTable<SomeTableModel>()
    group query by new { Year = query.CreationDate.Year, Month = query.CreationDate.Month, Day = query.CreationDate.Day }
    into list1
    select list1;

它将被翻译成:

SELECT
    [t1].[c1] as [c11],
    [t1].[c2] as [c21],
    [t1].[c3] as [c31]
FROM
    (
        SELECT
            DatePart(Year, [selectParam].[CreationDate]) as [c1],
            DatePart(Month, [selectParam].[CreationDate]) as [c2],
            DatePart(Day, [selectParam].[CreationDate]) as [c3]
        FROM
            [SomeDatabase.SomeTable] [selectParam]
    ) [t1]
GROUP BY
    [t1].[c1],
    [t1].[c2],
    [t1].[c3]

这是正确的查询.

我想实体框架试图优化我的查询或类似的东西,这就是为什么我有错误的查询.

我对吗？我是以正确的方式做到的吗？我该怎么办(可能使用直接SQL查询或其他东西)？

Answer 1

在这里使用EntityFunctions*要简单得多:

var result =
    from query in DbManager.GetTable<SomeTableModel>()
    group query by EntityFunctions.TruncateTime(query.CreationDate)
    into list1
    select list1;

^{*实体框架6中的DbFunctions.}

Answer 2

更新答案： EntityFunctions已弃用。

警告 1 'System.Data.Entity.Core.Objects.EntityFunctions' 已过时：'此类已被 System.Data.Entity.DbFunctions 取代。c:\users\liufa\documents\visual studio 2013\Projects\MatasMrLenderTest\Mvc5MobileApplication1\Controllers\CreditScoreController.cs 32 103 Mvc5MobileApplication1

现在是DbFunctions。

using System.Data.Entity;

var result = DbManager.GetTable<SomeTableModel>()
.GroupBy(o => DbFunctions.TruncateTime(o.CreationDate))