Hibernate Criteria 多层次查询关联问题

hibernate存在如下表及关联: 

class House{
  private string houseid;
  private string housename;
}
class Shelf{
  private string shelfid;
  private House house;
}
class Position{
  private string positionid;
  private Shelf shelf;
}
class Warehouse{
  private string warehouseid;
  private Position position;
}

Warehouse外键关联Pisition, Position外键关联Shelf, Shelf外键关联houseid。 
现在要对Warehouse使用Criteria查询, 查询House的id，可使用如下方法: 

Criteria criteria = BaseUtil.getCriteria(Warehouse.class);
criteria.createAlias("position", "position");
criteria.createAlias("position.shelf", "shelf");
criteria.add(Expression.eq("shelf.house.houseid", "111"));

如果要查询House的name, 必须再关联House表: 

Criteria criteria = BaseUtil.getCriteria(Warehouse.class);
criteria.createAlias("position", "position");
criteria.createAlias("position.shelf", "shelf");
criteria.createAlias("shelf.house", "house");
criteria.add(Expression.eq("house.housename", "name A"));

以上代码就可以实现了。 

可是还会出现一个问题:如果表路径position已经被关联过了(比如此criteria是传入的参数,已经关联了Alias路径position, 并查询过了),则会报错。解决方法： 
检查criteria里面关联的路径，如果已经关联，则不再关联，直接使用就行了。 

class CriteriaUtil{
public static Criteria addAlias(CriteriaImpl criteriaImpl, String path, String name){
  if(path == null) return criteriaImpl;
  for(Iterator iter = criteriaImpl.iterateSubcriteria();iter.hasNext();){
    Subcriteria subCriteria = (Subcriteria)iter.next();
    if(path.equals(subCriteria.getPath()))
      return criteriaImpl;
  }
  return criteriaImpl.createAlias(path, name);
}
}

(注：这段代码有时是存在问题的，不是所有的Criteria 都能转换为CriteriaImpl，可能会是Subcriteria。因此，需要确保传入的参数为CriteriaImpl) 

调用代码就变成： 

Criteria criteria = BaseUtil.getCriteria(Warehouse.class);
CriteriaUtil.addAlias((CriteriaImpl)criteria, "position", "position");
CriteriaUtil.addAlias((CriteriaImpl)criteria, "position.shelf", "shelf");
criteria.add(Expression.eq("shelf.house.houseid", "111"));