code: public function getModelsFromCustomRelationship($attributeName, $objName, $query = false, $loadMap = false)
       {
        // Create a repository for the related object.
        $repo = \Cora\RepositoryFactory::make($objName, false, false, false, $this->model_db);
        
        // Grab a Query Builder object for the connection this related model uses.
        // If no query object was passed in, then grab an appropriate one.
        if (!$query) $query = $this->_getQueryObjectForRelation($attributeName);
  
        // Grab the name of the method that defines the relationship
        $definingFunctionName = $this->model_attributes[$attributeName]['using'];
        
        // Pass query to the defining function
        $query = $this->$definingFunctionName($query);
        
        return $repo->findAll($query, false, $loadMap);
       }
docs: The Related Obj's are defined by a custom query. A "using" definition states which model
  method defines the relationship. Within that method any query parameters must bet set and
  a Query Builder object returned.