JPA关系映射之one-to-one
Posted SaraMorning
tags:
篇首语:本文由小常识网(cha138.com)小编为大家整理,主要介绍了JPA关系映射之one-to-one相关的知识,希望对你有一定的参考价值。
一对一关联有两种实现方式:一种是共享的主键关联,另一种是一对一的外键关联
1、共享的主键关联:让两个对象具有共同的主键值,以表明他们之间的一一对应关系。
Person.java类
1 public class Person implements java.io.Serializable { 2 3 // Fields 4 5 private Integer id; 6 private String name; 7 private Idcard idcard; 8 9 // Constructors 10 11 /** default constructor */ 12 public Person() { 13 } 14 15 /** full constructor */ 16 public Person(String name) { 17 this.name = name; 18 } 19 20 // Property accessors 21 22 public Integer getId() { 23 return this.id; 24 } 25 26 public void setId(Integer id) { 27 this.id = id; 28 } 29 30 public String getName() { 31 return this.name; 32 } 33 34 public void setName(String name) { 35 this.name = name; 36 } 37 public Idcard getIdcard() { 38 return idcard; 39 } 40 41 public void setIdcard(Idcard idcard) { 42 this.idcard = idcard; 43 } 44 }
Idcard.java类
1 public class Idcard implements java.io.Serializable { 2 3 // Fields 4 5 private Integer id; 6 private String idcardno; 7 private Person person; 8 9 // Constructors 10 11 /** default constructor */ 12 public Idcard() { 13 } 14 15 /** full constructor */ 16 public Idcard(String idcardno) { 17 this.idcardno = idcardno; 18 } 19 20 // Property accessors 21 22 public Integer getId() { 23 return this.id; 24 } 25 26 public void setId(Integer id) { 27 this.id = id; 28 } 29 30 public String getIdcardno() { 31 return this.idcardno; 32 } 33 34 public void setIdcardno(String idcardno) { 35 this.idcardno = idcardno; 36 } 37 38 public Person getPerson() { 39 return person; 40 } 41 42 public void setPerson(Person person) { 43 this.person = person; 44 } 45 46 }
Person.hbm.xml
1 <?xml version="1.0" encoding="utf-8"?> 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 3 "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> 4 <!-- 5 Mapping file autogenerated by MyEclipse Persistence Tools 6 --> 7 <hibernate-mapping> 8 <class name="com.db.entity.Person" table="person" catalog="mydb"> 9 <id name="id" type="java.lang.Integer"> 10 <column name="id" /> 11 <generator class="native" /> 12 </id> 13 <property name="name" type="java.lang.String"> 14 <column name="name" length="30" /> 15 </property> 16 <one-to-one name="idcard" class="com.db.entity.Idcard" cascade="all" /> 17 </class> 18 </hibernate-mapping>
Idcard.hbm.xml
1 <hibernate-mapping> 2 <class name="com.db.entity.Idcard" table="idcard" catalog="mydb"> 3 <id name="id" type="java.lang.Integer"> 4 <column name="id" /> 5 <generator class="foreign"> 6 <param name="property">person</param> 7 </generator> 8 </id> 9 <one-to-one name="person" constrained="true" class="com.db.entity.Person"></one-to-one> 10 <property name="idcardno" type="java.lang.String"> 11 <column name="idcardno" length="20" /> 12 </property> 13 </class> 14 </hibernate-mapping>
bibernate.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 <!-- Generated by MyEclipse Hibernate Tools. --> 6 <hibernate-configuration> 7 8 <session-factory> 9 <property name="dialect"> 10 org.hibernate.dialect.mysqlDialect 11 </property> 12 <property name="connection.url"> 13 jdbc:mysql://localhost:3306/mydb 14 </property> 15 <property name="connection.username">root</property> 16 <property name="connection.password">123456</property> 17 <property name="connection.driver_class"> 18 com.mysql.jdbc.Driver 19 </property> 20 <property name="myeclipse.connection.profile"> 21 MyDBAccount 22 </property> 23 <mapping resource="com/db/entity/Idcard.hbm.xml" /> 24 <mapping resource="com/db/entity/Person.hbm.xml" /> 25 </session-factory> 26 27 </hibernate-configuration>
测试代码:
1 public class TestOneOne { 2 3 public static void main(String[] args) { 4 // TODO Auto-generated method stub 5 6 Session session=null; 7 session=HibernateSessionFactory.getSession(); 8 session.beginTransaction(); 9 Idcard idcard=new Idcard(); 10 idcard.setIdcardno("2345678901"); 11 Person person=new Person(); 12 person.setName("Lily"); 13 person.setIdcard(idcard); 14 idcard.setPerson(person); 15 session.save(person); 16 session.save(idcard); 17 session.getTransaction().commit(); 18 19 } 20 21 }
2、一对一的外键关联:外键关联,本来是用于多对一的配置,但是加上唯一的限制之后(采用<many-to-one>标签来映射,指定多的一端unique为true,这样就限制了多的一端的多重性为一),也可以用来表示一对一关联关系,其实它就是多对一的特殊情况。
首先在表idcard中新添加一列pid用于共享数据
Person.java类
1 public class Person implements java.io.Serializable { 2 3 // Fields 4 5 private Integer pid; 6 private String name; 7 private Idcard idcard; 8 9 // Constructors 10 11 /** default constructor */ 12 public Person() { 13 } 14 15 /** full constructor */ 16 public Person(String name) { 17 this.name = name; 18 } 19 20 // Property accessors 21 22 public Integer getPid() { 23 return this.pid; 24 } 25 26 public void setPid(Integer pid) { 27 this.pid = pid; 28 } 29 30 public String getName() { 31 return this.name; 32 } 33 34 public void setName(String name) { 35 this.name = name; 36 } 37 public Idcard getIdcard() { 38 return idcard; 39 } 40 41 public void setIdcard(Idcard idcard) { 42 this.idcard = idcard; 43 } 44 }
idcard.java类
1 public class Idcard implements java.io.Serializable { 2 3 // Fields 4 5 private Integer iid; 6 private String idcardno; 7 private Person person; 8 9 // Constructors 10 11 /** default constructor */ 12 public Idcard() { 13 } 14 15 /** full constructor */ 16 public Idcard(String idcardno) { 17 this.idcardno = idcardno; 18 } 19 20 // Property accessors 21 22 public Integer getIid() { 23 return this.iid; 24 } 25 26 public void setIid(Integer iid) { 27 this.iid = iid; 28 } 29 30 public String getIdcardno() { 31 return this.idcardno; 32 } 33 34 public void setIdcardno(String idcardno) { 35 this.idcardno = idcardno; 36 } 37 38 public Person getPerson() { 39 return person; 40 } 41 42 public void setPerson(Person person) { 43 this.person = person; 44 } 45 46 }
Person.hbm.xml
1 <hibernate-mapping> 2 <class name="com.db.entity.Person" table="person" catalog="mydb"> 3 <id name="pid" type="java.lang.Integer"> 4 <column name="pid" /> 5 <generator class="native" /> 6 </id> 7 <property name="name" type="java.lang.String"> 8 <column name="name" length="30" /> 9 </property> 10 <one-to-one name="idcard" class="com.db.entity.Idcard" property-ref="person"></one-to-one> 11 </class> 12 </hibernate-mapping>
Idcard.hbm.xml
1 <hibernate-mapping> 2 <class name="com.db.entity.Idcard" table="idcard" catalog="mydb"> 3 <id name="iid" type="java.lang.Integer"> 4 <generator class="native"> 5 </generator> 6 </id> 7 <many-to-one name="person" column="pid" class="com.db.entity.Person" 8 cascade="save-update" unique="true"></many-to-one> 9 <property name="idcardno" type="java.lang.String"> 10 <column name="idcardno" length="20" /> 11 </property> 12 </class> 13 </hibernate-mapping>
bibernate.cfg.xml文件和测试代码同上。
如果使用注解映射外键,则注解如下:
Idcard.java类
1 public class Idcard implements java.io.Serializable { 2 3 // Fields 4 private Person person; 5 6 @OneToOne 7 @JoinColumn(name="pid") 8 public Person getPerson() { 9 return person; 10 } 11 12 public void setPerson(Person person) { 13 this.person = person; 14 } 15 16 }
Person.java类
1 public class Person implements java.io.Serializable { 2 3 // Fields 4 private Idcard idcard; 5 6 @OneToOne(mappedBy="person") 7 public Idcard getIdcard() { 8 return idcard; 9 } 10 11 public void setIdcard(Idcard idcard) { 12 this.idcard = idcard; 13 } 14 }
以上是关于JPA关系映射之one-to-one的主要内容,如果未能解决你的问题,请参考以下文章
Hibernate关系映射之many-to-many(多对多)