c# - Entity Framework 按日期分组并返回新类

Question

我正在使用 .NET 和 Entity Framework 。我想按没有时间部分的日期对表格进行分组。

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(我用的是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};
}

在此方法中，linq 转换为此 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，因为它不只按日期分组。

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;

它将被翻译成这样:

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 Entity Framework 试图优化我的查询或类似的东西，这就是我得到错误查询的原因。

我说的对吗？我这样做的方式正确吗？我应该怎么做(可能使用直接 SQL 查询或其他方式)？

Answer 1

使用EntityFunctions就简单多了* 此处:

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

^{* DbFunctions从 Entity Framework 6 开始。}