gistfile1.txt

            $data['feeds']['_ids'] = $this->request->data['feeds'];
            $calendars = TableRegistry::get('Calendars');
            $calendar = $calendars->newEntity($data, [
                'associated' => [
                    'Feeds',
                ],
            ]);
            debug($calendar);
            $calendars->save($calendar);

== debug ==
/src/Controller/Api/FeedsController.php (line 31)
object(App\Model\Entity\Calendar) {

	'feeds' => [
		(int) 0 => object(App\Model\Entity\Calendar) {

			'id' => (int) 37,
			'title' => 'TEST 2',
			'calendar_event_count' => null,
			'is_visible' => true,
			'api_key_id' => (int) 1,
			'color' => null,
			'created' => null,
			'modified' => null,
			'[new]' => false,
			'[accessible]' => [
				'*' => true
			],
			'[dirty]' => [],
			'[original]' => [],
			'[virtual]' => [],
			'[errors]' => [],
			'[invalid]' => [],
			'[repository]' => 'Feeds'
		
		},
		(int) 1 => object(App\Model\Entity\Calendar) {

			'id' => (int) 127,
			'title' => 'TEST 3',
			'calendar_event_count' => null,
			'is_visible' => true,
			'api_key_id' => (int) 1,
			'color' => null,
			'created' => null,
			'modified' => null,
			'[new]' => false,
			'[accessible]' => [
				'*' => true
			],
			'[dirty]' => [],
			'[original]' => [],
			'[virtual]' => [],
			'[errors]' => [],
			'[invalid]' => [],
			'[repository]' => 'Feeds'
		
		}
	],
	'[new]' => true,
	'[accessible]' => [
		'*' => true
	],
	'[dirty]' => [
		'feeds' => true
	],
	'[original]' => [],
	'[virtual]' => [],
	'[errors]' => [
		'title' => [
			'_required' => 'A title is required.'
		]
	],
	'[invalid]' => [],
	'[repository]' => 'Calendars'

}
===debug===