Hibernate学习25 -- 延迟加载2 -- 集合Lazy特征

<class>标签上的lazy不会影响到集合上的lazy特性，hibernate在集合上的lazy策略，可以取值：true/false/extra。代码实现：

CellectionlazyTest1.java

/**  * 保持lazy默认,class标签lazy为true ，set标签lazy为true *  */ public class CellectionlazyTest1 extends TestCase {         public void testLoad() {        Session session = null;        try {            session = HibernateUtils.getSession();            session.beginTransaction();                   //不会发出sql            Classes classes = (Classes)session.load(Classes.class,  1);            //会发出sql            System.out.println("classes.name=" + classes.getName());            //不会发出sql            Set students = classes.getStudents();                    //会发出sql            for (Iterator iter=students.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);        }     }

CellectionlazyTest2.java

/**  * 设置<class>标签上的lazy=false，set标签lazy为true  */ public class CellectionlazyTest2 extends TestCase {     public void testLoad() {        Session session = null;        try {            session = HibernateUtils.getSession();            session.beginTransaction();                   //会发出sql                Classes classes = (Classes)session.load(Classes.class, 1);            //不会发出sql            System.out.println("classes.name=" + classes.getName());            //不会发出sql            Set students = classes.getStudents();                    //会发出sql            for (Iterator iter=students.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);        }     }   }

CellectionlazyTest3.java

/**  * 设置集合上的lazy=false,其它默认  */ public class CellectionlazyTest3 extends TestCase {     public void testLoad1() {        Session session = null;        try {            session = HibernateUtils.getSession();            session.beginTransaction();            //不会发出sql            Classes classes = (Classes)session.load(Classes.class,  1);            //会发出sql,会发出两条sql分别加载Classes和Student            System.out.println("classes.name=" + classes.getName());            //不会发出sql            Set students = classes.getStudents();            //不会发出sql            for (Iterator iter=students.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);        }     } }

CellectionlazyTest4.java

/**  * 设置集合上的lazy=extra,其它默认  */ public class CellectionlazyTest4 extends TestCase {     public void testLoad1() {        Session session = null;        try {            session = HibernateUtils.getSession();            session.beginTransaction();            //不会发出sql            Classes classes = (Classes)session.load(Classes.class, 1);            //会发出sql            System.out.println("classes.name=" + classes.getName());            //不会发出sql            Set students = classes.getStudents();            //会发出sql            for (Iterator iter=students.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);        }     }       public void testLoad2() {        Session session = null;        try {            session = HibernateUtils.getSession();            session.beginTransaction();            //不会发出sql            Classes classes = (Classes)session.load(Classes.class, 1);            //会发出sql            System.out.println("classes.name=" + classes.getName());            //不会发出sql            Set students = classes.getStudents();            //会发出sql,发出一条比较智能的sql            //sql:select count(id) from t_student where classesid =?            System.out.println("student.count=" + students.size());            session.getTransaction().commit();        }catch(Exception e) {            e.printStackTrace();            session.getTransaction().rollback();        }finally {            HibernateUtils.closeSession(session);        }     }      }