How to group by week in Entity Framework Core?
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}";
}
}