Hibernate学习笔记——主键的配置

Hibernate的ID生成策略有很多种，具体的类型可以直接查阅Hibernate的doc。简单介绍一下几个常用的id。

Hibernate的配置文件：

<?xml version='1.0' encoding='utf-8'?><!DOCTYPE hibernate-configuration PUBLIC        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"><hibernate-configuration>    <session-factory>        <!-- Database connection settings -->               <property name="connection.driver_class">com.mysql.jdbc.Driver</property>        <property name="connection.url">jdbc:mysql://localhost:3306/hibernate</property>        <property name="connection.username">root</property>        <property name="connection.password">root</property>        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>                <!--         <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>        <property name="connection.url">jdbc:oracle:thin:@localhost:1521:HYLOCAL</property>        <property name="connection.username">HYLOCAL</property>        <property name="connection.password">123</property>        <property name="dialect">org.hibernate.dialect.Oracle10gDialect</property> -->        <!-- JDBC connection pool (use the built-in) -->        <!--  <property name="connection.pool_size">1</property>-->       <property name="javax.persistence.validation.mode">none</property> <!-- <property name="javax.persistence.validation.mode">none</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.internal.NoCacheProvider</property>        <!-- Echo all executed SQL to stdout -->        <property name="show_sql">true</property>        <!-- Drop and re-create the database schema on startup 这个配置会校验数据库 validate 创建表 create 更新表 update 结束后drop create-drop Automatically validates or exports schema DDL to the database when the SessionFactory is created. With create-drop, the database schema will be dropped when the SessionFactory is closed explicitly.  -->        <property name="hbm2ddl.auto">create</property>        <!-- <mapping resource="com/smile/hibernate/model/Student.hbm.xml"/> --><mapping class="com.smile.hibernate.model.Teacher"/>    </session-factory></hibernate-configuration>

1、单主键的配置：

Teacher.java：

package com.smile.hibernate.model;import java.util.Date;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.EnumType;import javax.persistence.Enumerated;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.Table;import javax.persistence.Temporal;import javax.persistence.TemporalType;@Entity@Table(name="Teacher")public class Teacher {private int id;private String name;private String title;private Date birthDate;private Title teacherTitle;@Enumerated(EnumType.STRING)public Title getTeacherTitle() {return teacherTitle;}public void setTeacherTitle(Title teacherTitle) {this.teacherTitle = teacherTitle;}//默认为datatime类型 @Temporal(TemporalType.DATE) TemporalType.TIME TemporalType.TIMESTAMPpublic Date getBirthDate() {return birthDate;}public void setBirthDate(Date birthDate) {this.birthDate = birthDate;}@Id@GeneratedValue(strategy=GenerationType.SEQUENCE)public int getId() {return id;}public void setId(int id) {this.id = id;}@Column(name="name")public String getName() {return name;}//不想持久化的时候 使用  @Transientpublic void setName(String name) {this.name = name;}public String getTitle() {return title;}public void setTitle(String title) {this.title = title;}}

这里使用的是注解的方式，首先一个实例需要添加注解@Entity才可以进行持久化。可以通过@Table的注解来指明对应的表名称，如果不指定则默认表名与类名一致。在主键的get方法或者是声明的地方用@Id来表名这是一个主键。同时使用

@GeneratedValue(strategy=GenerationType.SEQUENCE)

来指定ID的生成策略。

也可以使用一个表来存储主键，比较适合于跨数据库的服务：

package com.smile.hibernate;import java.util.Date;import javax.persistence.AttributeOverride;import javax.persistence.AttributeOverrides;import javax.persistence.Column;import javax.persistence.EmbeddedId;import javax.persistence.Entity;import javax.persistence.EnumType;import javax.persistence.Enumerated;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.IdClass;import javax.persistence.SequenceGenerator;import javax.persistence.Temporal;import javax.persistence.TemporalType;import javax.persistence.Transient;@Entitypublic class Teacher {private TeacherPK pk;private int id;private String name;private String title; private String yourWifeName;private Date birthDate;private boolean good;private Gender gender;@Enumerated(EnumType.STRING)@Column(name="t_sex")public Gender getGender() {return gender;}public void setGender(Gender gender) {this.gender = gender;}public boolean isGood() {return good;}public void setGood(boolean good) {this.good = good;}@Transientpublic String getYourWifeName() {return yourWifeName;}public void setYourWifeName(String yourWifeName) {this.yourWifeName = yourWifeName;}@Id @GeneratedValue(strategy=GenerationType.TABLE, generator="Teacher_GEN") @javax.persistence.TableGenerator(     name="Teacher_GEN",     table="GENERATOR_TABLE",     pkColumnName = "pk_key",     valueColumnName = "pk_value",     pkColumnValue="Teacher",     allocationSize=1 )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 String getTitle() {return title;}public void setTitle(String title) {this.title = title;}@Temporal(TemporalType.TIME)public Date getBirthDate() {return birthDate;}public void setBirthDate(Date birthDate) {this.birthDate = birthDate;}}

对于oracle来说也可以直接通过注解声明一个sequence，后面来使用：

@SequenceGenerator(name="teacherSEQ", sequenceName="teacherSEQ_DB")

2、联合主键的配置

联合主键的实现需要一个创建一个类来实现：

package com.smile.hibernate;import javax.persistence.Embeddable;@Embeddablepublic class TeacherPK implements java.io.Serializable{private int id;private String name;//@Column(name = "t_id")public int getId() {return id;}public void setId(int id) {this.id = id;}//@Column(name = "t_name")public String getName() {return name;}public void setName(String name) {this.name = name;}@Overridepublic boolean equals(Object o) {if(o instanceof TeacherPK) {TeacherPK pk = (TeacherPK)o;if(this.id == pk.getId() && this.name.equals(pk.getName())) {return true;}}return false;}@Overridepublic int hashCode() {return this.name.hashCode();}}

这个类有几个需要注意的地方：1、实现Serializable接口。2、重写equals方法用于判定主键的重复与否。3、重写hashCode方法已便于查找。同时添加注解@Embeddable。

修改Teacher.java：

package com.smile.hibernate;import java.util.Date;import javax.persistence.AttributeOverride;import javax.persistence.AttributeOverrides;import javax.persistence.Column;import javax.persistence.EmbeddedId;import javax.persistence.Entity;import javax.persistence.EnumType;import javax.persistence.Enumerated;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.IdClass;import javax.persistence.SequenceGenerator;import javax.persistence.Temporal;import javax.persistence.TemporalType;import javax.persistence.Transient;@Entitypublic class Teacher {private TeacherPK pk;private String title; private String yourWifeName;private Date birthDate;private boolean good;private Gender gender;@Enumerated(EnumType.STRING)@Column(name="t_sex")public Gender getGender() {return gender;}public void setGender(Gender gender) {this.gender = gender;}public boolean isGood() {return good;}public void setGood(boolean good) {this.good = good;}@Transientpublic String getYourWifeName() {return yourWifeName;}public void setYourWifeName(String yourWifeName) {this.yourWifeName = yourWifeName;}public String getTitle() {return title;}public void setTitle(String title) {this.title = title;}@Temporal(TemporalType.TIME)public Date getBirthDate() {return birthDate;}public void setBirthDate(Date birthDate) {this.birthDate = birthDate;}@EmbeddedId@AttributeOverrides( {@AttributeOverride(name = "id", column = @Column(name = "t_id")),@AttributeOverride(name = "name", column = @Column(name = "t_name")) }) public TeacherPK getPk() {return pk;}public void setPk(TeacherPK pk) {this.pk = pk;}}

在Teacher中添加TeacherPK类型的属性并且在get方法中增加注解@EmbeddedId。同时可以指定对应的列名。

还有另外一种实现方式：

package com.smile.hibernate;import java.util.Date;import javax.persistence.AttributeOverride;import javax.persistence.AttributeOverrides;import javax.persistence.Column;import javax.persistence.EmbeddedId;import javax.persistence.Entity;import javax.persistence.EnumType;import javax.persistence.Enumerated;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.IdClass;import javax.persistence.SequenceGenerator;import javax.persistence.Temporal;import javax.persistence.TemporalType;import javax.persistence.Transient;@Entity@IdClass(TeacherPK.class)public class Teacher {private TeacherPK pk;private int id;private String name;private String title; private String yourWifeName;private Date birthDate;private boolean good;private Gender gender;@Enumerated(EnumType.STRING)@Column(name="t_sex")public Gender getGender() {return gender;}public void setGender(Gender gender) {this.gender = gender;}public boolean isGood() {return good;}public void setGood(boolean good) {this.good = good;}@Transientpublic String getYourWifeName() {return yourWifeName;}public void setYourWifeName(String yourWifeName) {this.yourWifeName = yourWifeName;}@Idpublic int getId() {return id;}public void setId(int id) {this.id = id;}@Idpublic String getName() {return name;}public void setName(String name) {this.name = name;}public String getTitle() {return title;}public void setTitle(String title) {this.title = title;}@Temporal(TemporalType.TIME)public Date getBirthDate() {return birthDate;}public void setBirthDate(Date birthDate) {this.birthDate = birthDate;}}

在Teacher上添加注解:

@IdClass(TeacherPK.class)

同时指定id name为ID

然后也可以实现相同的效果。