標籤:span mit this throw service back 技術分享 begin 1對多
一、緩衝的概念:
以空間換時間; 二、Hibernate緩衝的分類: 前面我們講的緩衝都是session緩衝;也叫一級緩衝;get,load等緩衝都是內建的,一級緩衝;SessionFactory緩衝,二級緩衝;
這裡以Class —— Student,1對多的關係(單向)來例子說明下:
Class.java:
package com.cy.model;public class Class { private int id; private String name; 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; } }
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Student.java:
package com.cy.model;import com.cy.model.Class;public class Student { private int id; private String name; private Class c; 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 Class getC() { return c; } public void setC(Class c) { this.c = c; } }
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Class.hbm.xml:
<hibernate-mapping package="com.cy.model"> <class name="Class" table="t_class"> <id name="id" column="classId"> <generator class="native"></generator> </id> <property name="name" column="className"></property> </class></hibernate-mapping>
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Student.hbm.xml:
<hibernate-mapping package="com.cy.model"> <class name="Student" table="t_student"> <id name="id" column="stuId"> <generator class="native"></generator> </id> <property name="name" column="stuName"></property> <many-to-one name="c" class="com.cy.model.Class" column="classId" cascade="save-update"></many-to-one> </class></hibernate-mapping>
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StudentTest.java:
package com.cy.service;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.junit.After;import org.junit.Before;import org.junit.Test;import com.cy.model.Class;import com.cy.util.HibernateUtil;public class StudentTest { private SessionFactory sessionFactory=HibernateUtil.getSessionFactory(); private Session session; @Before public void setUp() throws Exception { session=sessionFactory.openSession(); session.beginTransaction(); } @After public void tearDown() throws Exception { session.getTransaction().commit(); session.close(); } /** * 同一個session中,同一個事務是有一級緩衝的; */ @Test public void testCache1(){ Class c = (Class) session.get(Class.class, 1); System.out.println(c.getName()); Class c2 = (Class) session.get(Class.class, 1); System.out.println(c2.getName()); System.out.println(c == c2); /* * Hibernate: select class0_.classId as classId1_0_0_, class0_.className as classNam2_0_0_ from t_class class0_ where class0_.classId=? 08電腦本科 08電腦本科 true 第一次取c1的時候,已經將取出來的資料c1放到緩衝中。 第二次取c2的時候,是有session緩衝的。首選從緩衝中找,找到,直接從緩衝中拿,而不到資料庫中去取了。 兩個是同一個OID對象; */ } /** * 在不同的事務中,是否有緩衝? */ @Test public void testCache2(){ Session session1 = sessionFactory.openSession(); session1.beginTransaction(); Class c = (Class) session1.get(Class.class, 1); System.out.println(c.getName()); session1.getTransaction().commit(); session1.close(); Session session2 = sessionFactory.openSession(); session2.beginTransaction(); Class c2 = (Class) session2.get(Class.class, 1); System.out.println(c2.getName()); session2.getTransaction().commit(); session2.close(); System.out.println(c == c2); /* * Hibernate: select class0_.classId as classId1_0_0_, class0_.className as classNam2_0_0_ from t_class class0_ where class0_.classId=? 08電腦本科 Hibernate: select class0_.classId as classId1_0_0_, class0_.className as classNam2_0_0_ from t_class class0_ where class0_.classId=? 08電腦本科 false 雖然在同一個session中有緩衝,但是這裡新開闢了一個事務,發出兩個sql 不同的事務是不能共用一級緩衝的。 一級緩衝只適用於同一個session,同一個事務; */ }}
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三、二級緩衝策略供應商:
Hibernate學習11——配置Hibernate二級緩衝