hibernate 带条件外关联检索的方法

原文地址: http://blog.youkuaiyun.com/jxc/archive/2006/12/29/1467550.aspx

想在hibernate里实现如下SQL:

select   *
   from  t_join_a a
   left   outer   join  t_join_a_b c  on  a.a_id  =  c.a_id  and  c.b_id  =   ' b2 '
  where  a.a_name  is   not   null

需要解决2个问题: 外关联和外关联中的条件, 希望下面的内容能够节省大家学习的时间

需要做下面的工作:

public   class  T_join_a  ... {
    private String a_id;

    private String a_name;

    private Set t_join_b;
    
    private Set t_join_a_b;

    // 省略 getter/setter
}



public   class  T_join_a_b  implements  Serializable ... {

    private static final long serialVersionUID = 8337568440339952023L;

    private String a_id;

    private String b_id;

    private String t_join_a;

    private String t_join_b;

    // 省略 getter/setter

}


public   class  T_join_b  ... {
    private String b_id;

    private String b_name;

    private Set t_join_a;

//     省略 getter/setter
}

 

HBM.XML配置如下:

 

<? xml version="1.0" ?>
<! DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"  >

< hibernate-mapping  package ="demo.hibernate.join" >
     < class  name ="T_join_a"  table ="t_join_a" >
         < id  name ="a_id"  column ="a_id"  type ="string" >
             < generator  class ="org.hibernate.id.UUIDHexGenerator"   />
         </ id >
         < property  name ="a_name"  column ="a_name"  type ="string"   />
        
         <!--  通过 1对多 关联 t_join_a_b  -->
         < set  name ="t_join_a_b"  table ="t_join_a_b"  lazy ="true"  inverse ="true"
            cascade ="all"   >             
             < key  column ="a_id"   />
             < one-to-many  class ="T_join_a_b"   />
         </ set >
        
         <!--  通过多对多关联 t_join_b  -->
         < set  name ="t_join_b"  table ="t_join_a_b"  lazy ="true"  inverse ="false"
            cascade ="save-update" >
             < key >
                 < column  name ="a_id"   />
             </ key >
             < many-to-many  class ="T_join_b"  column ="b_id"  
                outer-join ="auto"   />
         </ set >
        
     </ class >

</ hibernate-mapping >

 

<? xml version="1.0" ?>
<! DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"  >

< hibernate-mapping  package ="demo.hibernate.join" >
     < class  name ="T_join_a_b"  table ="t_join_a_b" >
         < composite-id >
             < key-property  name ="a_id"  column ="a_id"  type ="string"   />
             < key-property  name ="b_id"  column ="b_id"  type ="string"   />             
         </ composite-id >

         < many-to-one  name ="t_join_a"  class ="T_join_a"  cascade ="none"
            outer-join ="auto"  update ="false"  insert ="false"  access ="property"
            column ="a_id"  not-null ="true"   />

     </ class >

</ hibernate-mapping >

 

<? xml version="1.0" ?>
<! DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"  >

< hibernate-mapping  package ="demo.hibernate.join" >
     < class  name ="T_join_b"  table ="t_join_b" >
         < id  name ="b_id"  column ="b_id"  type ="string" >
             < generator  class ="org.hibernate.id.UUIDHexGenerator"   />
         </ id >
         < property  name ="b_name"  column ="b_name"  type ="string"   />

        
         < set  name ="t_join_a"  table ="t_join_a_b"  lazy ="true"  inverse ="false"
            cascade ="save-update" >
             < key >
                 < column  name ="b_id"   />
             </ key >
             < many-to-many  class ="T_join_a"  column ="a_id"
                outer-join ="auto"   />
         </ set >
     </ class >

</ hibernate-mapping >

 

最后HQL语法如下, hibernate里外关联不能写 on , 其中外关联里的条件是通过 hibernate 的 with 关键字实现的 :

select  new Map(a.a_id  as  a_id,a.a_name  as  a_name, c.b_id  as  b_id) 
  from  T_join_a a   left   outer   join  a.t_join_a_b c 
   with  c.b_id  =   ' b2 '

 

主要的java代码如下:

String hql;
Query query;
Iterator it;

hql  =   " select new Map(a.a_id as a_id,a.a_name as a_name, c.b_id as b_id)  "
       +   "  from T_join_a a  "   +   "  left outer join a.t_join_a_b c  "  
       +   "  with c.b_id = 'b2' " ;

query  =  session.createQuery(hql);
it  =  query.list().iterator();
while  (it.hasNext())  ... {
    Map map = (Map) it.next();

    System.out.print("a_id : " + map.get("a_id"));
    System.out.println("  b_id : " + map.get("b_id"));
}