Hibernate 一对一映射之主键关联 Annotation Example
0.pom.xml
......
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<hibernate-version>3.6.10.Final</hibernate-version>
<javassist-version>3.12.1.GA</javassist-version>
<slf4j-nop-version>1.6.6</slf4j-nop-version>
<mysql-connector-version>5.1.21</mysql-connector-version>
</properties>
<dependencies>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>${hibernate-version}</version>
</dependency>
<dependency>
<groupId>javassist</groupId>
<artifactId>javassist</artifactId>
<version>${javassist-version}</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-nop</artifactId>
<version>${slf4j-nop-version}</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>${mysql-connector-version}</version>
</dependency>
</dependencies>
......
1.schema.sql
drop table if exists idcard; drop table if exists student; create table idcard ( iid integer not null, num integer, primary key (iid) ); create table student ( sid integer not null auto_increment, name varchar(255), primary key (sid) );
表结构如下图所示
2.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>
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost:3306/test</property>
<property name="connection.username">root</property>
<property name="connection.password">123456</property>
<property name="dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="show_sql">true</property>
<property name="format_sql">false</property>
<!-- <mapping resource="org/fool/model/Student.hbm.xml" /> -->
<!-- <mapping resource="org/fool/model/IdCard.hbm.xml" /> -->
<mapping class="org.fool.model.Student" />
<mapping class="org.fool.model.IdCard" />
</session-factory>
</hibernate-configuration>
这里使用Student表和IdCard表进行一对一关联
3.Student.java
package org.fool.model;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.Table;
import org.hibernate.annotations.Fetch;
import org.hibernate.annotations.FetchMode;
@Entity
@Table(name = "student")
public class Student {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "sid")
private int id;
@Column(name = "name")
private String name;
@OneToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "student")
@Fetch(FetchMode.SELECT)
private IdCard idCard;
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 IdCard getIdCard() {
return idCard;
}
public void setIdCard(IdCard idCard) {
this.idCard = idCard;
}
}
以上的annotation就相当于以下的Student.hbm.xml文件，可以进行对比一下
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="org.fool.model.Student" table="student"> <id name="id" column="sid" type="integer"> <generator class="identity"> </generator> </id> <property name="name" column="name" type="string" /> <one-to-one name="idCard" class="org.fool.model.IdCard" cascade="all" fetch="select"></one-to-one> </class> </hibernate-mapping>
4.IdCard.java
package org.fool.model;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.PrimaryKeyJoinColumn;
import javax.persistence.Table;
import org.hibernate.annotations.Fetch;
import org.hibernate.annotations.FetchMode;
import org.hibernate.annotations.GenericGenerator;
import org.hibernate.annotations.Parameter;
@Entity
@Table(name = "idcard")
public class IdCard {
@Id
@GenericGenerator(name = "generator", strategy = "foreign",
parameters = @Parameter(name = "property", value = "student"))
@GeneratedValue(generator = "generator")
@Column(name = "iid")
private int id;
@Column(name = "num")
private int num;
@OneToOne(fetch = FetchType.LAZY)
@PrimaryKeyJoinColumn
@Fetch(FetchMode.SELECT)
private Student student;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public int getNum() {
return num;
}
public void setNum(int num) {
this.num = num;
}
public Student getStudent() {
return student;
}
public void setStudent(Student student) {
this.student = student;
}
}
以上的annotation就相当于以下的IdCard.hbm.xml文件，可以进行对比一下
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="org.fool.model.IdCard" table="idcard"> <id name="id" column="iid" type="integer"> <generator class="foreign"> <param name="property">student</param> </generator> </id> <property name="num" column="num" type="integer" /> <one-to-one name="student" class="org.fool.model.Student" fetch="select"></one-to-one> </class> </hibernate-mapping>
5.HibernateUtil.java
package org.fool.util;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HibernateUtil {
private static SessionFactory sessionFactory;
static {
try {
sessionFactory = new Configuration().configure()
.buildSessionFactory();
} catch (Exception ex) {
System.err.println("构造SessionFactory异常发生： " + ex.getMessage());
}
}
public static Session openSession() {
Session session = sessionFactory.openSession();
return session;
}
public static void closeSession(Session session) {
if (null != session) {
session.close();
}
}
}
6.HibernateTest.java
package org.fool.test;
import org.fool.model.IdCard;
import org.fool.model.Student;
import org.fool.util.HibernateUtil;
import org.hibernate.Session;
import org.hibernate.Transaction;
public class HibernateTest {
public static void main(String[] args) throws Exception {
// insert();
// selectStudent();
// updateStudent();
// delete();
}
/**
* 添加信息
*/
public static void insert() {
Session session = HibernateUtil.openSession();
Transaction tx = null;
try {
tx = session.beginTransaction();
Student student = new Student();
student.setName("zhangsan");
IdCard idCard = new IdCard();
idCard.setNum(123456);
student.setIdCard(idCard);
idCard.setStudent(student);
session.save(student);
tx.commit();
} catch (Exception e) {
e.printStackTrace();
if (null != tx) {
tx.rollback();
}
} finally {
HibernateUtil.closeSession(session);
}
}
/**
* 查询学生信息
*/
public static void selectStudent() {
Session session = HibernateUtil.openSession();
Transaction tx = null;
Student student = null;
try {
tx = session.beginTransaction();
student = (Student) session.get(Student.class, 1);
tx.commit();
} catch (Exception e) {
e.printStackTrace();
if (null != tx) {
tx.rollback();
}
} finally {
HibernateUtil.closeSession(session);
}
System.out.println(student.getName());
System.out.println(student.getIdCard().getNum());
}
/**
* 更新学生信息
*/
public static void updateStudent() {
Session session = HibernateUtil.openSession();
Transaction tx = null;
Student student = null;
try {
tx = session.beginTransaction();
student = (Student) session.get(Student.class, 1);
student.setName("lisi");
tx.commit();
} catch (Exception e) {
e.printStackTrace();
if (null != tx) {
tx.rollback();
}
} finally {
HibernateUtil.closeSession(session);
}
System.out.println(student.getName());
}
/**
* 级联删除
*/
public static void delete() {
Session session = HibernateUtil.openSession();
Transaction tx = null;
Student student = null;
try {
tx = session.beginTransaction();
student = (Student) session.get(Student.class, 1);
session.delete(student);
tx.commit();
} catch (Exception e) {
e.printStackTrace();
if (null != tx) {
tx.rollback();
}
} finally {
HibernateUtil.closeSession(session);
}
}
}
7.总结
主键关联：一对一默认使用的是立即加载，如果需要使用延迟加载，那么需要在one-to-one元素中将constrained属性设为true，并且将待加载的一方的class元素中lazy属性设为true（或者不去设置，因为该属性默认值是true）；一对一加载时默认 使用左外连接，可以通过修改fetch属性为select，修改成每次发送一条select语句的形式。