How to GroupBy week in Entity Framework in PostgreSQL

Question

I have a table which has column DateTime. And I want to group this by week. There are no problem to group by date or by month. But how to group by week?

I need to get something like this. And in should work with IQueryable.

var peoplePerWeeks = await context.People
                                  .GroupBy(x => x.Date.StartOfWeek)
                                  .Select(x => new { Date = x.key, Number = x.Count()})
                                  .ToListAsync();

Answer 1

tried anything like? (this is just my example data, no postgres or entity framework, see last note, but you want to group on week start )

var people = new List<(DateTime Date, string fullName)> {
    ( new DateTime(2022, 3, 1), "fred"),
    ( new DateTime(2022, 3, 2), "b"),
    ( new DateTime(2022, 3, 3), "c"),
    ( new DateTime(2022, 3, 4), "d"),
    ( new DateTime(2022, 3, 5), "e"),
    ( new DateTime(2022, 3, 9), "f")
  };

  var groupWeek = people.GroupBy(x => {
    var td = x.Date;
    while (td.DayOfWeek != System.DayOfWeek.Monday) td = td.AddDays(-1);
    return td;
  }).Select(x => new { WeekStart = x.Key, Count = x.Count(), dataList = x.ToList() });

  var myList = groupWeek.ToList();

the part that does what you mention, I think, is

 people.GroupBy(x => {
    var td = x.Date;
    while (td.DayOfWeek != System.DayOfWeek.Monday) td = td.AddDays(-1);
    return td;
  })

with your start day of week in there as appropriate to you