所有项目导入对应的hibernate的jar包、mysql的jar包和添加每次都需要用到的HibernateUtil.java
第一节:Hibernate 用对象标识符(OID)来区分对象
例子:
hibernate.cfg.xml
1 <?xml version='1.0' encoding='utf-8'?> 2 <!DOCTYPE hibernate-configuration PUBLIC 3 "-//Hibernate/Hibernate Configuration DTD 3.0//EN" 4 "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"> 5 6 <hibernate-configuration> 7 8 <session-factory> 9 10 <!--数据库连接设置 --> 11 <property name="connection.driver_class">com.mysql.jdbc.Driver</property> 12 <property name="connection.url">jdbc:mysql://localhost:3306/hibernate</property> 13 <property name="connection.username">root</property> 14 <property name="connection.password">123456</property> 15 16 17 <!-- 方言 --> 18 <property name="dialect">org.hibernate.dialect.MySQL5Dialect</property> 19 20 <!-- 控制台显示SQL --> 21 <property name="show_sql">true</property> 22 23 <!-- 自动更新表结构 --> 24 <property name="hbm2ddl.auto">update</property> 25 26 <mapping resource="com/wishwzp/model/Student.hbm.xml"/> 27 28 </session-factory> 29 30 </hibernate-configuration>
Student.java
1 package com.wishwzp.model; 2 3 public class Student { 4 5 private long id; 6 private String name; 7 8 public long getId() { 9 return id; 10 } 11 public void setId(long id) { 12 this.id = id; 13 } 14 public String getName() { 15 return name; 16 } 17 public void setName(String name) { 18 this.name = name; 19 } 20 @Override 21 public String toString() { 22 return "Student [id=" + id + ", name=" + name + "]"; 23 } 24 25 26 }
Student.hbm.xml
1 <?xml version="1.0"?> 2 <!DOCTYPE hibernate-mapping PUBLIC 3 "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 4 "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> 5 6 <hibernate-mapping package="com.wishwzp.model"> 7 8 <class name="Student" table="t_student"> 9 <id name="id" column="stuId"> 10 <generator class="native"></generator> 11 </id> 12 13 <property name="name"></property> 14 </class> 15 16 </hibernate-mapping>
StudentTest.java
1 package com.wishwzp.service; 2 3 import org.hibernate.Session; 4 import org.hibernate.SessionFactory; 5 6 import com.wishwzp.model.Student; 7 import com.wishwzp.util.HibernateUtil; 8 9 public class StudentTest { 10 11 public static void main(String[] args) { 12 SessionFactory sessionFactory=HibernateUtil.getSessionFactory(); 13 Session session=sessionFactory.openSession(); // 生成一个session 14 session.beginTransaction(); // 开启事务 15 16 //获取主键为1的学生 17 Student s1=(Student)session.get(Student.class, Long.valueOf(1));//当执行到这里的时候Session缓冲中会有OID为1的Studnet对象 18 //获取主键为2的学生 19 Student s2=(Student)session.get(Student.class, Long.valueOf(2));//当执行到这里的时候Session缓冲中会有OID为2的Studnet对象 20 //获取主键为1的学生 21 Student s3=(Student)session.get(Student.class, Long.valueOf(1));//在Session缓冲中找到了UID为1,所以指向了UID为1的对象 22 System.out.println(s1==s2);//false 23 System.out.println(s1==s3);//true 24 session.getTransaction().commit(); // 提交事务 25 session.close(); // 关闭session 26 } 27 }
这是数据库的信息:
结果显示:
这就表明S1和S3是指向一个地址的
第二节:Hibernate 对象标识符生成策略
主键的分类
业务主键VS 代理主键
代理主键是不具有业务性的;
1,increment 由Hibernate 自动以递增的方式生成标识符,适用代理主键;
2,identity 由底层数据库生成标识符;适用代理主键;
3,sequcence 由Hibernate 根据底层数据库的序列来生成标识符;适用代理主键;
4,hilo Hibernate 根据high/low 算法来生成标识符。适用代理主键
5,native 根据底层数据库对自动生成标识符的支持能力, 来选择identity,sequence 或hilo;适用代理主键;
increment 例子:
hibernate.cfg.xml
1 <?xml version='1.0' encoding='utf-8'?> 2 <!DOCTYPE hibernate-configuration PUBLIC 3 "-//Hibernate/Hibernate Configuration DTD 3.0//EN" 4 "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"> 5 6 <hibernate-configuration> 7 8 <session-factory> 9 10 <!--数据库连接设置 --> 11 <property name="connection.driver_class">com.mysql.jdbc.Driver</property> 12 <property name="connection.url">jdbc:mysql://localhost:3306/hibernate</property> 13 <property name="connection.username">root</property> 14 <property name="connection.password">123456</property> 15 16 17 <!-- 方言 --> 18 <property name="dialect">org.hibernate.dialect.MySQL5Dialect</property> 19 20 <!-- 控制台显示SQL --> 21 <property name="show_sql">true</property> 22 23 <!-- 自动更新表结构 --> 24 <property name="hbm2ddl.auto">update</property> 25 26 <mapping resource="com/wishwzp/model/Student.hbm.xml"/> 27 28 </session-factory> 29 30 </hibernate-configuration>
Student.java
1 package com.wishwzp.model; 2 3 public class Student { 4 5 private long id; 6 private String name; 7 8 public long getId() { 9 return id; 10 } 11 public void setId(long id) { 12 this.id = id; 13 } 14 public String getName() { 15 return name; 16 } 17 public void setName(String name) { 18 this.name = name; 19 } 20 @Override 21 public String toString() { 22 return "Student [id=" + id + ", name=" + name + "]"; 23 } 24 25 26 }
Student.hbm.xml
1 <?xml version="1.0"?> 2 <!DOCTYPE hibernate-mapping PUBLIC 3 "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 4 "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> 5 6 <hibernate-mapping package="com.wishwzp.model"> 7 8 <class name="Student" table="t_student"> 9 <id name="id" column="stuId"> 10 <generator class="increment"></generator> 11 </id> 12 13 <property name="name"></property> 14 </class> 15 16 </hibernate-mapping>
StudentTest2.java
1 package com.wishwzp.service; 2 3 import org.hibernate.Session; 4 import org.hibernate.SessionFactory; 5 6 import com.wishwzp.model.Student; 7 import com.wishwzp.util.HibernateUtil; 8 9 public class StudentTest2 { 10 11 public static void main(String[] args) { 12 SessionFactory sessionFactory=HibernateUtil.getSessionFactory(); 13 Session session=sessionFactory.openSession(); // 生成一个session 14 session.beginTransaction(); // 开启事务 15 16 Student s=new Student(); 17 s.setName("张三"); 18 session.save(s); 19 20 session.getTransaction().commit(); // 提交事务 21 session.close(); // 关闭session 22 } 23 }
结果显示:
当我继续在执行一下代码。。。。。
结果显示:
identity 例子:
increment 例子的代码只改变一下Student.hbm.xml,其他什么代码都不改变。
Student.hbm.xml
1 <?xml version="1.0"?> 2 <!DOCTYPE hibernate-mapping PUBLIC 3 "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 4 "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> 5 6 <hibernate-mapping package="com.wishwzp.model"> 7 8 <class name="Student" table="t_student"> 9 <id name="id" column="stuId"> 10 <generator class="identity"></generator> 11 </id> 12 13 <property name="name"></property> 14 </class> 15 16 </hibernate-mapping>
结果显示:
当我继续在执行一下代码。。。。。
结果显示:
native 例子:
increment 例子的代码只改变一下Student.hbm.xml,其他什么代码都不改变。
Student.hbm.xml
1 <?xml version="1.0"?> 2 <!DOCTYPE hibernate-mapping PUBLIC 3 "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 4 "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> 5 6 <hibernate-mapping package="com.wishwzp.model"> 7 8 <class name="Student" table="t_student"> 9 <id name="id" column="stuId"> 10 <generator class="native"></generator> 11 </id> 12 13 <property name="name"></property> 14 </class> 15 16 </hibernate-mapping>
结果显示:
当我继续在执行一下代码。。。。。
结果显示:
主要native用的最多。