第 16 章 条件查询(Criteria Queries) http://oss.org.cn/ossdocs/framework/hibernate/reference-v3_zh-cn/querycriteria.html
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"));