Hibernate配置及三种Id生成策略_hibernate hbm id-优快云博客

本文链接：https://blog.youkuaiyun.com/cjsxjm/article/details/50997238

本文主要探讨了Hibernate的学习重点，包括Id的生成策略，如默认策略、sequence策略和uuid策略，同时还涉及到了hibernate的配置、表的关联关系、基本的CRUD操作以及优化方面的内容。

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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

@Entity
public class Customer {

@Id 
@GeneratedValue
Integer getId() { ... };
}

@Entity
public 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....