如何在Entity Framework Core中按周分组？ [英] How to group by week in Entity Framework Core?

问题描述

在Entity Framework 6中，我可以使用 SqlFunctions。 DatePart（） 方法：

  var byWeek = data.GroupBy（x => ; SqlFunctions.DatePart（week，x.Date））; 
  

但是这些类（ DbFunctions 和 SqlFunctions 在实体框架核心中不可用）（参考）。

所以我的问题是如何在Entity Framework核心中按周分组？

解决方案

我缺少的功能的当前解决方法是

  var firstMondayOfYear = this.GetFirstMondayOfYear（DateTime.Now.Year）; 
 var entries = 
 this.entitiesService.FindForLastMonths（this.CurrentUser.Id，6）
 .GroupBy（x =>（（int）（x.Date  -  firstMondayOfYear）.TotalDays / 7））
  

函数 GetFirstMondayOfYear ：

  private DateTime GetFirstMondayOfYear（int year）
 {
 var dt = new DateTime（year，1，1 ）; 
 while（dt.DayOfWeek！= DayOfWeek.Monday）
 {
 dt = dt.AddDays（1）; 
} 
 
 return dt; 
} 
  

此分组给出当年的周数和前几年的负值。

稍后，您可以使用此getter获取星期名称：

  public string WeekName 
 {
 get 
 {
 var year = DateTime.Now.AddYears（（int）Math.Floor（this.WeekNumber / 52.0））。 
 var weekNumber = this.WeekNumber％52; 
 while（weekNumber <0）
 {
 weekNumber + = 52; 
} 
 
返回${year}，W {weekNumber}; 
} 
} 
  

In Entity Framework 6 I can use SqlFunctions.DatePart() method:

var byWeek = data.GroupBy(x => SqlFunctions.DatePart("week", x.Date));

But these classes (DbFunctions and SqlFunctions are not available in Entity Framework Core) (reference).

So my question is How can I group by week in Entity Framework core?

解决方案

My current workaround for the missing functionality is

var firstMondayOfYear = this.GetFirstMondayOfYear(DateTime.Now.Year);
var entries =
    this.entitiesService.FindForLastMonths(this.CurrentUser.Id, 6)
        .GroupBy(x => ((int)(x.Date - firstMondayOfYear).TotalDays / 7))

The function GetFirstMondayOfYear:

private DateTime GetFirstMondayOfYear(int year)
{
    var dt = new DateTime(year, 1, 1);
    while (dt.DayOfWeek != DayOfWeek.Monday)
    {
        dt = dt.AddDays(1);
    }

    return dt;
}

This grouping gives the week number for the current year and negative values for previous years.

Later you can get the week name by using this getter:

public string WeekName
{
    get
    {
        var year = DateTime.Now.AddYears((int)Math.Floor(this.WeekNumber / 52.0)).Year;
        var weekNumber = this.WeekNumber % 52;
        while (weekNumber < 0)
        {
            weekNumber += 52;
        }

        return $"{year}, W{weekNumber}";
    }
}

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