/**
  * Adds a related model.
  */
 public function add(RedBeanModel $model)
 {
     assert("\$model instanceof {$this->modelClassName}");
     assert('!$this->contains($model)');
     assert('($oldCount = $this->count()) > -1');
     // To save the value only when asserts are enabled.
     $bean = $model->getClassBean($this->modelClassName);
     $this->deferredRelateBeans[] = $bean;
     if (in_array($bean, $this->deferredUnrelateBeans)) {
         self::array_remove_object($this->deferredUnrelateBeans, $bean);
     }
     $this->relatedBeansAndModels[] = $model;
     $this->modified = true;
     assert('$this->count() == $oldCount + 1');
     assert('$this->contains($model)');
 }