SilverStripe: Sorting DataObject with has_many relation - silverstripe

Question

In SilverStripe I have a event dataobject
class Event extends DataObject {
private static $db = array(
'Name' => 'Text'
);
private static $has_many = array(
'EventDates' => 'EventDate'
that has many event dates:
class EventDate extends DataObject {
private static $db = array(
'Day' => 'Date',
'StartTime' => 'Varchar',
'EndTime' => 'Varchar'
);
Now if I query all events on a page like
Event::get()
I want them to be sorted by the earliest date.
Which way is the best to achieve this?

Answer 1

You can define a static property on the DataObject class with a default sort rule:
<?php
class EventDate extends DataObject {
…
// This also effects the default sorting of `has_many` related Events.
private static $default_sort = "\"Day\" ASC";
}
?>
Now
<?php
// first we pick a Event object, for instance by a (given) $id
$event = Event::get()->byId($id);
// because the default sort ist Day the attached `EventDate` will now be sorted by `Day` if you don't specify otherwise
$events = $event->EventDates();
// will return the earliest Event (of course you don't filter events here which are in the past).
$firstEvent = $events->First();
// if you then want to sort differently at some place, you can call ->sort() on the list:
$event = Event::get()->byId($id);
$events = $event->EventDates()->sort('LastEdited', 'DESC');
$lastEditedEvent = $events->First();
?>