Hibernate 中的addEntity()方法使用

 

[转]hibernate SQLQuery addEntity

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

自己的：

 

List<Object> objects=(List<Object>)session.createSQLQuery("select {s.*},{c.*} from student s,clazz c where s.clazz_id=c.c_id")
  .addEntity("s", Student.class).addEntity("c",Clazz.class).list();
  
  Iterator iterator=objects.iterator();
  
  while(iterator.hasNext()) {
   
   Object[] o=(Object[]) iterator.next();
   Student student=(Student) o[0];
   Clazz clazz=(Clazz) o[1];
   System.out.println(student.getName()+","+clazz.getTeacher());
  }

 

 

按照原博主的做法，一直有类型转换异常，所以只能用这方方法，求指教

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

 

来源:http://hi.baidu.com/gacmotor/item/65053176a02a545b0c0a07eb