Silverstripe add/save object to has_one relation

Question

I cannot find a clue on how to correctly save a has_one relation in Silverstripe.

class Car extends DataObject {
  $has_one = array(
     'garage'=>'Garage';
  );
}

class Garage extends DataObject {
  $has_many = array(
     'cars'=>'Car';
  );
}
// let's say I have these records in the DB
$g = Garage::get()->ByID(111);
$c = Car::get()->ByID(222);

// I want to do sth like this to define the relation
$c->Garage = $g;
$c->write();

But this code does nothing, no error, but also the relation is not created in the DB.

What I could to is this:

$c->GarageID = $g->ID;
$c->write();

But this does not seem very ORM like...

Answer 1

there doesn't seem to be an extra method for adding has_one relations, but if you want to stick with the ORM, you could do it the other way around:

$g->cars()->add($c);

Answer 2

This question is especially relevant if you have no corresponding has_many relationship, but want to establish an unsaved relationship between two objects.

What worked for me was creating a property, under the initial class, and assigning the unsaved relating object against that. The major limitations are:

• Your reference to the most current instance of the object needs to always be the property, otherwise you'll get concurency issues.
• Large objects being asigned will weigh down your available memory.

Fortunately, my case was a very simple object.

Example:

Car.php:

. . .

private static $has_one = array(
    'Garage' => 'Garage'
);

private $unsaved_relation_garage;

protected function onBeforeWrite() {

    parent::onBeforeWrite();

    // Save the unsaved relation too
    $garage = $this->unsaved_relation_garage;

    // Check for unsaved relation
    // NOTE: Unsaved relation will override existing
    if($garage) {

        // Check if garage already exists in db
        if(!$garage->exists()) {

            // If not, write garage
            $garage->write();
        }

        $this->GarageID = $garage->ID;
    }
}

/**
 * setGarage() will assign a written garage to this object's has_one 'Garage',
 * or an unwritten garage to $this->unsaved_relation_garage. Will not write.
 *
 * @param Garage $garage
 * @return Car
 */
public function setGarage($garage) {

    if($garage->exists()) {
        $this->GarageID = $garage->ID;
        return $this;
    }

    $this->unsaved_relation_garage = $garage;
    return $this;
}

/**
 * getGarage() takes advantage of the variation in method names for has_one relationships,
 * and will return $this->unsaved_relation_garage or $this->Garage() dependingly.
 *
 * @return Garage
 */
public function getGarage() {

    $unsaved = $this->unsaved_relation_garage;

    if($unsaved) {
        return $unsaved;
    }

    if($this->Garage()->exists()) {
        return $this->Garage();
    }

    return null;
}

. . .