code: protected function createRelationQuery($class, $foreignKey, $localKey, $multiple)
      {
          /* @var $class BaseBitrixModel */
          /* @var $query BaseQuery */
          $query = $class::query();
          $query->foreignKey = $localKey;
          $query->localKey = $foreignKey;
          $query->primaryModel = $this;
          $query->multiple = $multiple;
          return $query;
      }
docs: Creates a query instance for `has-one` or `has-many` relation.
  @param string $class the class name of the related record.
  @param string $foreignKey
  @param string $localKey
  @param bool $multiple whether this query represents a relation to more than one record.
  @return BaseQuery the relational query object.
  @see hasOne()
  @see hasMany()