A collection as a Koyomi calendar: each record on the day of the view's date field, a mark for each, and the records of the day a person picks.

<Cardbox.Koyomi.calendar id="due" view={@view} on_change="day" months={2} />

def handle_event("koyomi:days", %{"id" => "due"} = params, socket),
  do: Cardbox.Koyomi.handle_days(socket, params, MyApp.Cardbox, socket.assigns.collection, socket.assigns.view)

def handle_event("day", %{"value" => day}, socket) do
  {:ok, records} = Cardbox.Koyomi.on_day(MyApp.Cardbox, socket.assigns.collection, socket.assigns.view, day)
  {:noreply, assign(socket, day_records: records)}
end

The view is a saved Cardbox.View of type calendar: its date_field names the date field (a day, or a moment), and its query which records. The calendar asks for the days it shows a month or a few at a time, and the database reads only the records of those days.

A day's marks are a dot for each record (four at most), toned by the group of the record's status when the collection has one: to do muted, doing in the accent, done in green. Its title, read by screen readers and shown on hover, has the records' titles.

When records change (Cardbox.Event), Koyomi.Live.refresh_days/2 asks the calendar for its days again (Koyomi 0.2.1 and later, which Cardbox requires: before it, a refresh emptied the calendar).