Hibernate关联关系映射之一对一关联关系
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人和身份证之间就是一个典型的一对一关联关系。实现一对一关联关系映射的方式有两种一种是基于外键,一种是基于主键,下面我们先看基于外键的关联方式
首先看他们的实体类
Person类
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package entity; public class Person { private Integer id; private String name ; private IdCard idCard; public Integer getId() { return id; } public void setId( Integer 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; } } |
然后看IdCard类
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package entity; public class IdCard { private Integer id; private String number; private Person person; public Integer getId() { return id; } public void setId( Integer id) { this.id = id; } public String getNumber() { return number; } public void setNumber(String number) { this.number = number; } public Person getPerson() { return person; } public void setPerson(Person person) { this.person = person; } } |
这里在Person类和IdCard类中分别有一个对方类型的属性。
然后看他们之间的关联关系映射,首先看Person.hbm.xml
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<?xml version= "1.0" encoding= "utf-8" ?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" <hibernate-mapping> <class name = "entity.Person" table = "Person" schema = "MYHR" > <id name = "id" type= "int" > < column name = "ID" /> <generator class= "assigned" /> </id> <property name = "name" type= "string" > < column name = "NAME" not - null = "true" /> </property> <! -- idCard属性,IdCard类型,表达本类与IdCard的一对一关联 --> <! -- 采用基于外键的一对一,本方无外键方 --> <! -- property-ref属性:对方映射中外键类对应的属性名 --> <one- to -one name = "idCard" class= "entity.IdCard" property-ref= "person" > </one- to -one> </class> </hibernate-mapping> |
然后看一下IdCard.hbm.xml文档
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<?xml version= "1.0" encoding= "utf-8" ?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" <hibernate-mapping> <class name = "entity.IdCard" table = "IdCard" schema = "MYHR" > <id name = "id" > < column name = "ID" /> <generator class= "assigned" /> </id> <property name = "number" > < column name = "NAME" not - null = "true" /> </property> <! -- person属性,Person类型,表示与Person类的一对一关联关系 --> <! -- 采用基于外键的一对一关联方式,本方有外键 --> <many- to -one name = "person" column = "personId" class= "entity.Person" unique = "true" ></many- to -one> </class> </hibernate-mapping> |
这样Person和IdCard之间的一对一关联关系就搭建好了,然后看一下测试类
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package test; import static org.junit.Assert.*; import org.hibernate.Session; import org.hibernate. Transaction ; import entity.IdCard; import entity.Person; import factory.HibernateSessionFactory; public class Test { private Session session = null ; private Transaction tran = null ; @org.junit.Test public void save() { session = HibernateSessionFactory.getSession(); tran = session.beginTransaction(); try{ //新建对象 Person p = new Person(); p.setId(1); p.setName( "张三" ); IdCard idCard = new IdCard(); idCard.setId(1); idCard.setNumber( "10001" ); p.setIdCard(idCard); idCard.setPerson(p); session.save(p); session.save(idCard); tran. commit (); }catch(Exception e){ tran. rollback (); } } @org.junit.Test public void Get() { session = HibernateSessionFactory.getSession(); tran = session.beginTransaction(); try{ Person person = (Person) session.get(Person.class, 1); IdCard idCard = person.getIdCard(); System. out .println(person.getName()+ "身份证号:" +idCard.getNumber()); tran. commit (); }catch(Exception e){ tran. rollback (); } } //解除关系 @org.junit.Test public void RemoveRelation() { session = HibernateSessionFactory.getSession(); tran = session.beginTransaction(); try{ //从有外键方接触关联关系可以,不可以从无外键方解除 IdCard idCard = (IdCard)session.get(IdCard.class, 1); idCard.setPerson( null ); tran. commit (); }catch(Exception e){ tran. rollback (); } } //删除 @org.junit.Test public void DeleteRelation() { session = HibernateSessionFactory.getSession(); tran = session.beginTransaction(); try{ //如果没有关联对方,可以直接删除。 //如果有关联对方,且可以维护关联关系,他就会先删除关联关系,在删除自己。 //如果有关联关系,且不能维护关联关系,所以会执行删除自己,并且抛出异常。 IdCard idCard = (IdCard)session.get(IdCard.class, 1); session. delete (idCard); tran. commit (); }catch(Exception e){ tran. rollback (); } } } |
这就是基于外键方式,基于主键的方式只需要在以上基础修改一下映射文件即可,下面分别看一下修改后的映射文件
首先看Person.hbm.xml
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<?xml version= "1.0" encoding= "utf-8" ?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" <hibernate-mapping package= "entity" > <class name = "entity.Person" table = "Person" schema = "MYHR" > <id name = "id" type= "int" > < column name = "ID" /> <generator class= "assigned" /> </id> <property name = "name" type= "string" > < column name = "NAME" not - null = "true" /> </property> <! -- idCard属性,IdCard类型,表达本类与IdCard的一对一关联 --> <! -- 采用基于主键的一对一,本方无外键方 --> <one- to -one name = "idCard" class= "entity.IdCard" /> </class> </hibernate-mapping> |
然后看IdCard.hbm.xml
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<?xml version= "1.0" encoding= "utf-8" ?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" <hibernate-mapping package= "entity" > <class name = "entity.IdCard" table = "IdCard" schema = "MYHR" > <id name = "id" type= "int" > < column name = "ID" /> <! -- 当使用基于主键的一对一映射时,有外键方的主键生成策略是foreign, --> <! -- 参数property:生成主键值时所根据的对象 --> <generator class= "foreign" > <param name = "property" >person</param> </generator> </id> <property name = "number" type= "string" > < column name = "NAME" not - null = "true" /> </property> <! -- person属性,Person类型,表示与Person类的一对一关联关系 --> <! -- 采用基于主键的一对一关联方式,本方有外键 --> <one- to -one name = "person" class= "entity.Person" constrained= "true" /> </class> </hibernate-mapping> |
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