hibernate 集合上的lazy策略

hibernate 集合上的lazy策略
2011年09月01日
　　 hibernate在集合上的lazy策略，可以取值：true/false/extra 
　　标签上的lazy不会影响到集合上的lazy特性 
　　建议将集合上的lazy设置成extra 
　　1.实体类 
　　package com.yx.zzg.bo; import java.util.Set; public class Classes { private int id; private String name; private Set students; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Set getStudents() { return students; } public void setStudents(Set students) { this.students = students; } } 
　　package com.yx.zzg.bo; public class Student { private int id; private String name; private Classes classes; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Classes getClasses() { return classes; } public void setClasses(Classes classes) { this.classes = classes; } } 
　　2.实体类映射文件 
　　           
　　              
　　3.测试类1：CellectionlazyTest1.java 
　　package com.yx.zzg.test; import java.util.HashSet; import java.util.Iterator; import java.util.Set; import com.yx.zzg.bo.*; import junit.framework.TestCase; import org.hibernate.Session; /** * 保持lazy默认 * @author Administrator * */ public class CellectionlazyTest1 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,发出查询全部数据的sql System.out.println("student.count=" + students.size()); session.getTransaction().commit(); }catch(Exception e) { e.printStackTrace(); session.getTransaction().rollback(); }finally { HibernateUtils.closeSession(session); } } } 
　　测试类2：CellectionlazyTest2.java 
　　package com.yx.zzg.test; import java.util.HashSet; import java.util.Iterator; import java.util.Set; import com.yx.zzg.bo.*; import junit.framework.TestCase; import org.hibernate.Session; /** * 设置标签上的lazy=false * @author Administrator * */ public class CellectionlazyTest2 extends TestCase { public void testLoad1() { 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); } } } 
　　测试类3：CellectionlazyTest3.java 
　　package com.yx.zzg.bo; import java.util.HashSet; import java.util.Iterator; import java.util.Set; import com.yx.zzg.bo.* import junit.framework.TestCase; import org.hibernate.Session; /** * 设置集合上的lazy=false,其它默认 * @author Administrator * */ 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); } } 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,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 System.out.println("student.count=" + students.size()); session.getTransaction().commit(); }catch(Exception e) { e.printStackTrace(); session.getTransaction().rollback(); }finally { HibernateUtils.closeSession(session); } } } 
　　测试类4：CellectionlazyTest4.java 
　　package com.yx.zzg.test; import java.util.HashSet; import java.util.Iterator; import java.util.Set; import com.yx.zzg.bo.*; import junit.framework.TestCase; import org.hibernate.Session; /** * 设置集合上的lazy=extra,其它默认 * @author Administrator * */ 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 System.out.println("student.count=" + students.size()); session.getTransaction().commit(); }catch(Exception e) { e.printStackTrace(); session.getTransaction().rollback(); }finally { HibernateUtils.closeSession(session); } } }