Hibernate query.addEntity 转载+原创

 

hibernate SQLQuery addEntity

2010-07-08 09:52

 

两个表(实体), 1对多双向关联: 班级: Clazz (id, name) 学生: Student(id, name , class_id) 1. 查询持久化对象   1.1 简单查询，返回数据库结构 view plaincopy to clipboardprint? sql = "select c.* from clazz c,student s where s.class_id = c.id";         List<Clazz> clazzs = (List<Clazz>)session.createSQLQuery(sql).list();   sql = "select c.* from clazz c,student s where s.class_id = c.id"; List<Clazz> clazzs = (List<Clazz>)session.createSQLQuery(sql).list(); 特别注意：返回结果是Object[]组成的List，通过Object下标访问属性 使用场合：非基于对象的查询，复杂查询 1.2 简单查询，返回持久化对象 sql = "select c.* from Clazz c , student s where s.class_id = c.id ";    List<Clazz> clazzs = (List<Clazz>) session.createSQLQuery(sql).addEntity(Clazz.class).list(); 特别注意： 1.addEntity方法指定返回包含Clazz对象的List 2. 查询出来的持久态对象，clazz对象的studets属性是各代理对象，访问的时候才会去查询DB 使用场合：基于对象的查询，但对象简单查询 1.3 多表查询，返回多个实体 view plaincopy to clipboardprint? String sql = "select {c.*}, {s.*} from Clazz c , student s where s.class_id = c.id   ";      List<Clazz> clazzs = (List<Clazz>) session().createSQLQuery(sql)                                       .addEntity("c", Clazz.class)                                       .addEntity("s", Student.class).list();   String sql = "select {c.*}, {s.*} from Clazz c , student s where s.class_id = c.id   "; List<Clazz> clazzs = (List<Clazz>) session().createSQLQuery(sql) .addEntity("c", Clazz.class) .addEntity("s", Student.class).list(); view plaincopy to clipboardprint? 特别注意：    1. addEntity方法指定了当前返回实体的别名,而且在SQL语句里使用{c.*}这样的语句,   它的意思是向别名为c的这个对象注入所有属性值.   特别注意： 1. addEntity方法指定了当前返回实体的别名,而且在SQL语句里使用{c.*}这样的语句, 它的意思是向别名为c的这个对象注入所有属性值. view plaincopy to clipboardprint? 2. 这个查询会返回一个Object的List,每个Object包含两个对象一个Clazz,一个Student   view plaincopy to clipboardprint? 3. {}占位符里是对象的属性,而非列名,如{s.class},而非{s.class_id}   view plaincopy to clipboardprint? 4. 必须注入对象的每个属性值，你可以使用{c.*}，或者手工写全所有，但必须是所有属性。（这个太让我郁闷了。    view plaincopy to clipboardprint? 使用场合：基于对象的查询，复杂查询   1.4 多表查询，返回关联实体 view plaincopy to clipboardprint? String sql = "select {c.*}, {s.*} from Clazz c , student s where s.class_id = c.id   ";      List<Clazz> clazzs = (List<Clazz>) session().createSQLQuery(sql)              .addEntity("c", Clazz.class)              .addJoin("s", "c.students").list();   String sql = "select {c.*}, {s.*} from Clazz c , student s where s.class_id = c.id   "; List<Clazz> clazzs = (List<Clazz>) session().createSQLQuery(sql) .addEntity("c", Clazz.class) .addJoin("s", "c.students").list(); view plaincopy to clipboardprint? <p>特别注意: 这块有些问题，明明应该返回Clazz的List的,但确返回包含Clazz和Student的Object的List, faint</p><p>使用场合：基于对象的查询，复杂查询</p>   2. 查询托管对象 view plaincopy to clipboardprint? String sql = "select c.id, c.name from Clazz c , student s where s.class_id = c.id   ";         List<Clazz> clazzs = (List<Clazz>) session.createSQLQuery(sql)                                                 .addScalar("id", Hibernate.LONG)                                           .addScalar("name", Hibernate.STRING)                                                .setResultTransformer(Transformers.aliasToBean(Clazz.class)).list();   String sql = "select c.id, c.name from Clazz c , student s where s.class_id = c.id   "; List<Clazz> clazzs = (List<Clazz>) session.createSQLQuery(sql) .addScalar("id", Hibernate.LONG) .addScalar("name", Hibernate.STRING) .setResultTransformer(Transformers.aliasToBean(Clazz.class)).list(); 特别注意: 1. 如果不设置addScalar方法可能会报转型错误的异常. 2.托管查询可以使用投影,只查询指定的列属性 ==================================================华丽分割====以上为转载 http://blog.sina.com.cn/s/blog_5fcdcbf70100lfuq.html===== 以下为运用之后的，加入了查询。 Query query = this.getSession().createSQLQuery("select {em.*},{pc.*},{dept.*},{p.*} " + "from t_postcount pc ,t_post p ,t_employees em ,t_department dept " + "where pc.post = p.id and pc.epid = em.id and p.pid = dept.id " + "and em.id = "+employeesId+" order by dept.id,pc.date desc ") .addEntity("em",Employees.class) .addEntity("pc",PostCount.class) .addEntity("dept",Department.class) .addEntity("p",Post.class); List<Object[]> l = query.list(); List list = new ArrayList(); for(int i=0;i<l.size();i++){ PostCountBean pcb = new PostCountBean(); pcb.setName(((Employees)l.get(i)[0]).getName()); pcb.setDate(( (PostCount)l.get(i)[1]).getDate()); pcb.setDname(( (Department)l.get(i)[2]).getName()); pcb.setPname(( (Post)l.get(i)[3]).getName()); pcb.setPostNum(( (PostCount)l.get(i)[1]).getPostNum()); System.out.print (((Employees)l.get(i)[0]).getName()); System.out.print (( (PostCount)l.get(i)[1]).getDate()); System.out.print (( (Department)l.get(i)[2]).getName()); System.out.println(( (Post)l.get(i)[3]).getName()); list.add(pcb); }