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
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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
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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();
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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.
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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  
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3. {}占位符里是对象的属性,而非列名,如{s.class},而非{s.class_id}  
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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。   
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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

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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();
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<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

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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);}