code: private function defineManyToManyRelation(Model $model1, Model $model2) {
          //$this->app['log']->info(sprintf('%s has and belongs to many %s', $model1->getName(), str_plural($model2->getName())));
          $this->relations[$model1->getName()][] = new Relation($model1, $model2, Relation::HAS_AND_BELONGS_TO);
          $this->relations[$model2->getName()][] = new Relation($model2, $model1, Relation::HAS_AND_BELONGS_TO);
      }
docs: Defines a many-to-many relation between given models.
  
  @param $model1 Model the first model.
  @param $model2 Model the second model.