34hibernate_fetch_5_set_subselect

hibernate抓取策略（集合代理的批量抓取）

设置fetch="subselect",如：
<set name="students" inverse="true" cascade="all" fetch="subselect">

fetch="subselect",另外发送一条select语句抓取在前面查询到的所有实体对象的关联集合
============================================================================
testFetch1:

public void testFetch1() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
            Classes classes = (Classes)session.load(Classes.class, 1);
            System.out.println("classes.name=" + classes.getName());
            for (Iterator iter=classes.getStudents().iterator(); iter.hasNext();) {
                Student student = (Student)iter.next();
                System.out.println("student.name=" + student.getName());
            }
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }
Hibernate: select classes0_.id as id0_0_, classes0_.name as name0_0_ from t_classes classes0_ where classes0_.id=?
classes.name=班级0
Hibernate: select students0_.classesid as classesid1_, students0_.id as id1_, students0_.id as id1_0_, students0_.name as name1_0_, students0_.classesid as classesid1_0_ from t_student students0_ where students0_.classesid=?
student.name=班级0的学生6
student.name=班级0的学生1
student.name=班级0的学生5
student.name=班级0的学生4
student.name=班级0的学生0
student.name=班级0的学生2
student.name=班级0的学生3

====================================影响hql查询=======================================
testFetch2:

/**
     * Hibernate: select students0_.classesid as classesid1_, students0_.id as id1_, 
     * students0_.id as id1_0_, students0_.name as name1_0_, 
     * students0_.classesid as classesid1_0_ 
     * from t_student students0_ 
     * where students0_.classesid in (select classes0_.id from t_classes classes0_ where classes0_.id in (1 , 2 , 3))
     */
    public void testFetch2() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
            
            List classesList = session.createQuery("select c from Classes c where c.id in(1, 2, 3)").list();
            for (Iterator iter=classesList.iterator(); iter.hasNext();) {
                Classes classes = (Classes)iter.next();
                System.out.println("classes.name=" + classes.getName());
                for (Iterator iter1=classes.getStudents().iterator(); iter1.hasNext();) {
                    Student student = (Student)iter1.next();
                    System.out.println("student.name=" + student.getName());
                }
            }
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }

设置：<set name="students" inverse="true" cascade="all">    
Hibernate: select classes0_.id as id0_, classes0_.name as name0_ from t_classes classes0_ where classes0_.id in (1 , 2 , 3)
classes.name=班级0
Hibernate: select students0_.classesid as classesid1_, students0_.id as id1_, students0_.id as id1_0_, students0_.name as name1_0_, students0_.classesid as classesid1_0_ from t_student students0_ where students0_.classesid=?
student.name=班级0的学生2
student.name=班级0的学生1
student.name=班级0的学生6
student.name=班级0的学生5
student.name=班级0的学生4
student.name=班级0的学生3
student.name=班级0的学生0
classes.name=班级1
Hibernate: select students0_.classesid as classesid1_, students0_.id as id1_, students0_.id as id1_0_, students0_.name as name1_0_, students0_.classesid as classesid1_0_ from t_student students0_ where students0_.classesid=?
student.name=班级1的学生2
student.name=班级1的学生0
student.name=班级1的学生5
student.name=班级1的学生6
student.name=班级1的学生4
student.name=班级1的学生1
student.name=班级1的学生3
classes.name=班级2
Hibernate: select students0_.classesid as classesid1_, students0_.id as id1_, students0_.id as id1_0_, students0_.name as name1_0_, students0_.classesid as classesid1_0_ from t_student students0_ where students0_.classesid=?
student.name=班级2的学生2
student.name=班级2的学生0
student.name=班级2的学生3
student.name=班级2的学生1
student.name=班级2的学生4
student.name=班级2的学生6
student.name=班级2的学生5

    
设置：<set name="students" inverse="true" cascade="all" fetch="subselect">    
Hibernate: select classes0_.id as id0_, classes0_.name as name0_ from t_classes classes0_ where classes0_.id in (1 , 2 , 3)
classes.name=班级0
Hibernate: select students0_.classesid as classesid1_, students0_.id as id1_, students0_.id as id1_0_, students0_.name as name1_0_, students0_.classesid as classesid1_0_ from t_student students0_ where students0_.classesid in (select classes0_.id from t_classes classes0_ where classes0_.id in (1 , 2 , 3))
student.name=班级0的学生2
student.name=班级0的学生1
student.name=班级0的学生5
student.name=班级0的学生6
student.name=班级0的学生4
student.name=班级0的学生0
student.name=班级0的学生3
classes.name=班级1
student.name=班级1的学生4
student.name=班级1的学生5
student.name=班级1的学生3
student.name=班级1的学生2
student.name=班级1的学生6
student.name=班级1的学生0
student.name=班级1的学生1
classes.name=班级2
student.name=班级2的学生5
student.name=班级2的学生4
student.name=班级2的学生0
student.name=班级2的学生3
student.name=班级2的学生1
student.name=班级2的学生6
student.name=班级2的学生2