Pimcore\Model\Object\Fieldcollection::save PHP Method

    public function save($object)
    {
        $this->getDao()->save($object);
        $allowedTypes = $object->getClass()->getFieldDefinition($this->getFieldname())->getAllowedTypes();
        $collectionItems = $this->getItems();
        if (is_array($collectionItems)) {
            $index = 0;
            foreach ($collectionItems as $collection) {
                if ($collection instanceof Fieldcollection\Data\AbstractData) {
                    if (in_array($collection->getType(), $allowedTypes)) {
                        $collection->setFieldname($this->getFieldname());
                        $collection->setIndex($index++);
                        // set the current object again, this is necessary because the related object in $this->object can change (eg. clone & copy & paste, etc.)
                        $collection->setObject($object);
                        $collection->save($object);
                    } else {
                        throw new \Exception("Fieldcollection of type " . $collection->getType() . " is not allowed in field: " . $this->getFieldname());
                    }
                }
            }
        }
    }