Hibernate配置及三种Id生成策略

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hibernate的学习主要有：

1.Id的生成策略

2.表的关联关系

3.增删改查

4.优化

1.再说hibernate的Id生成策略之前，我们先来说一说hibernate的配置。

hibernate的配置默认的文件名为hibernate.cfg.xml。

<?xml version='1.0' encoding='utf-8'?><!DOCTYPE hibernate-configuration PUBLIC        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"><hibernate-configuration>    <session-factory>        <!-- Database connection settings 建立数据库的连接-->        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>        <property name="connection.url">jdbc:mysql://localhost/studentManage</property>        <property name="connection.username">root</property>        <property name="connection.password">123456</property>                <property name="connection.useUnicode">true</property>         <property name="connection.characterEncoding">UTF-8</property>        <!-- JDBC connection pool (use the built-in) -->        <property name="connection.pool_size">1</property>        <!-- SQL dialect 数据库方言-->        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>        <!-- Enable Hibernate's automatic session context management -->        <property name="current_session_context_class">thread</property>        <!-- Disable the second-level cache  -->        <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>        <!-- Echo all executed SQL to stdout是否打印出sql语句 -->         <property name="show_sql">true</property>        <!-- Drop and re-create the database schema on startup是否覆盖旧表，新建新表 -->         <!--<property name="hbm2ddl.auto">create</property>-->         <!-- <mapping resource="com/hibernate/Teacher.hbm.xml"/>将实体与数据库的表建立对应 -->        <mapping class="com.SM.table.UserLogin"></mapping>        <mapping class="com.SM.table.AcademyTable"></mapping>        <mapping class="com.SM.table.ClassTable"></mapping>        <mapping class="com.SM.table.StudentTable"></mapping>        <mapping class="com.SM.table.CourseTable"></mapping>        <mapping class="com.SM.table.GradeTable"></mapping>    </session-factory></hibernate-configuration>

2.Id生成策略

2.1 默认的Id生成策略

@Entitypublic class Customer {@Id @GeneratedValueInteger getId() { ... };}

@Entitypublic class Invoice {@Id @GeneratedValue(strategy=GenerationType.IDENTITY)Integer getId() { ... };}

2.2 采用sequence的生成策略

@Id@GeneratedValue(strategy=GenerationType.SEQUENCE,generator="SEQ_GEN")@javax.persistence.SequenceGenerator(name="SEQ_GEN",sequenceName="my_sequence",allocationSize=20)public Integer getId() { ... }

2.3 uuid的生成策略

@Id@GeneratedValue(generator="system-uuid")@GenericGenerator(name="system-uuid", strategy = "uuid")public String getId() {

以上的三种Id生成策略已经够用....

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