Set hasOne relation to new instance of child model

问题

Using Laravel 4.2, how can I set a hasOne relation on a model to an instance of a new model without touching the database?

I want to do the following, but Laravel is treating the instance as a property, not a child relation.

class ParentClass extends \Eloquent {
  public function child() {
    return $this-hasOne('ChildClass', 'child_id', 'parent_id');
  }
}

$parent = new ParentClass();
$parent->child = new ChildClass();

回答1:

To get through my problem, I have created a Trait class that I added to my models that allows me to set a relation. Doing this does not automatically set my parent/child relation values so I have to be careful to do this manually before I save/push.

trait ModelSetRelationTrait
{
  public function setRelation($key, $model)
  {
    $this->relations[$key] = $model;
  }
}

class ParentClass extends \Eloquent {
  use ModelSetRelationTrait;
  public function child() {
    return $this-hasOne('ChildClass', 'child_id', 'parent_id');
  }
}

来源：https://stackoverflow.com/questions/43416180/set-hasone-relation-to-new-instance-of-child-model