How to group by week in Entity Framework Core?

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?

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}";
    }
}