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