Hibernate一对一关联

一对一单向外键关联

1.建Husband实体类和Wife实体类，添加Annotation注解，如下

@Entitypublic class Husband {PRivate int id;private String name;private Wife wife;        @Id@GeneratedValuepublic 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;}@OneToOne                   //Husband和Wife是一对一的关系public Wife getWife() {return wife;}public void setWife(Wife wife) {this.wife = wife;}}

@Entitypublic class Wife {private int id;private String name;@Id@GeneratedValuepublic 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;}}

2.在hibernate.cfg.xml中添加mapping语句

<mapping class="com.hibernate.model.Husband"/> <mapping class="com.hibernate.model.Wife"/>

3.建Junit测试类

public class ORMappingTest {@Testpublic void test() {//生成表，输出建表语句new SchemaExport(new Configuration().configure()).create(true, true);}}

程序至此结束，运行程序，在数据库中生成Husband表和Wife表，并在控制台输出建表语句。

Husband表中会自动生成属性名为“wife_id”的外键，参考表为Wife表。

如果想要使用自定义的外键属性名，可对Husband实体类的getWife方法添加Annotation注解，如下：

@OneToOne   //Husband和Wife是一对一的关系@JoinColumn(name="wifeId")  // java默认生成的外键属性名为wife_id.设置此项后，可以任意设定其属性名，此处设置为wifeId.public Wife getWife() {return wife;}

一对一双向外键关联

1.建Husband实体类和Wife实体类，添加Annotation注解

Husband类同上，只需在Wife类中增加一个Husband类型的变量，并添加@OneToOne注解即可，如下

@Entitypublic class Wife {private int id;private String name;private Husband husband;   //建一个Husband类型的变量，并生成setter和getter方法 @Id@GeneratedValuepublic 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;}@OneToOne(mappedBy="wife")     //"wife"指的是Husband类中的private Wife wife;public Husband getHusband() {return husband;}public void setHusband(Husband husband) {this.husband = husband;}}

凡是双向关联，必设mappedBy

2.在hibernate.cfg.xml中添加mapping语句----同上

3.建Junit测试类----同上

程序至此结束，运行程序，在数据库中生成Husband表和Wife表，并在控制台输出建表语句。

联合主键

联合主键（3种方式）    将主键类注解为@Embeddable，并将主键(pk)的属性注解为@Id (不常用)    将主键的属性注解为@EmbeddedId      将实体类注解为@IdClass(组件类.class)，并将该实体类中所有属于主键的属性都注解为@Id

示例：建Wife表，属性有id，name，age。其中id和name为联合主键

1.建主键类WifePK

/* * 建立主键类WifePK * 需实现Serializable接口，此接口用于把当前类的接口进行序列化 * 需重写equals()和hashCode()方法，以保证对象的唯一性 *   **/public class WifePK implements java.io.Serializable{private int id;private String name;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;}@Overridepublic boolean equals(Object o){if(o instanceof WifePK){WifePK pk = (WifePK) o;if(this.id == pk.getId() && this.name.equals(pk.getName())){return true;}}return false;}@Overridepublic int hashCode(){return this.name.hashCode();}}

2.建实体类Wife

第二种方式注解，@EmbeddedId

@Entitypublic class Wife {private WifePK pk;    //增加WifePK类型的变量，并添加getter和setter方法private int age;@EmbeddedId              //将其注解为联合主键public WifePK getPk() {return pk;}public void setPk(WifePK pk) {this.pk = pk;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}}

第三种方式注解，@IdClass

@Entity@IdClass(WifePK.class)   //将实体类注解为@IdClasspublic class Wife {private int id;private String name;private int age;@Id               //将该实体类中属于主键的属性注解为@Id public int getId() {return id;}public void setId(int id) {this.id = id;}@Id                //将该实体类中属于主键的属性注解为@Id public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}}

3.写Junit测试类

第二种方式注解，@EmbeddedId

public class WifeTest {private static sessionFactory sf = null;@BeforeClasspublic static void beforeClass() {sf = new Configuration().configure().buildSessionFactory();}@AfterClasspublic static void afterClass() {sf.close();}@Testpublic void test() {WifePK pk = new WifePK();pk.setId(1);pk.setName("zhangsan");Wife wife = new Wife();wife.setPk(pk);wife.setAge(32);Session session = sf.getCurrentSession();session.beginTransaction();session.save(wife);session.getTransaction().commit();}}

第三种方式注解，@IdClass，只需修改其test()方法，如下：

@Testpublic void test() {Wife wife = new Wife();wife.setId(1);wife.setName("zhangsan");wife.setAge(32);Session session = sf.getCurrentSession();session.beginTransaction();session.save(wife);session.getTransaction().commit();}

程序至此结束，运行程序，在数据库中生成Wife表，id和name为主键，并将对象wife存入Wife表。

联合主键关联

示例：

建Husband表，属性有id和name

建Wife表，属性有id，name，age。其中id和name为联合主键

设置联合主键关联，在Husband表中生成属性名为wife_id和wife_name的外键，分别参考Wife表中的id和name

1.建Husband实体类、Wife实体类和WifePK主键类，添加Annotation注解

Husband类，同上

WifePK类，同上

Wife类，同“联合主键”部分第三种方式注解的Wife实体类

2.在hibernate.cfg.xml中添加mapping语句----同上

3.建Junit测试类ORMappingTest----同上

程序至此结束，运行程序，在数据库中生成Husband表和Wife表，并在控制台输出建表语句。

Husband表中会自动生成属性名为“wife_id”和“wife_name”的外键，参考表为Wife表。

如果想要使用自定义的外键属性名，可对Husband实体类的getWife方法添加Annotation注解，如下：

@OneToOne@JoinColumns({@JoinColumn(name="wifeId",referencedColumnName="id"),@JoinColumn(name="wifeName",referencedColumnName="name")})public Wife getWife() {return wife;}

组件映射

除了粗粒度的对象模型设计(一个表映射成一个持久化类)之外，还可以采用细粒度的对象模型，把一个表映射成两个或者多个类。

被细化出来的类，可以称为组件(Component)。

组件是某个实体的逻辑组成部分，它与实体的本质区别在于组件没有id，可以把组件当做值对象。

举例来说：Husband类有id、name、wifeName、wifeAge等属性，将wifeName、wifeAge从Husband实体类中拿出来，单独建一个Wife类，这个类就叫做值对象，也就是所说的组件。表现在数据库中，将只有husband一张表，有id、name、wifeName、wifeAge属性。

采用组件映射的优点：实现了对象细粒度的划分，层次更加分明，复用率高。

1.建立Husband实体类和Wife组件类，添加Annotation注解

Husband类同上，只是不需要添加@OneToOne注解，改为@Embedded注解，如下：

@Embeddedpublic Wife getWife() {return wife;}

Wife类无需添加任何注解，如下：

public class Wife {private String wifeName;private int wifeAge;public String getWifeName() {return wifeName;}public void setWifeName(String wifeName) {this.wifeName = wifeName;}public int getWifeAge() {return wifeAge;}public void setWifeAge(int wifeAge) {this.wifeAge = wifeAge;}}

2.在hibernate.cfg.xml中添加mapping语句

只需添加Husband的mapping，Wife类不是实体类，无需添加。

3.建Junit测试类ORMappingTest----同上

程序至此结束，运行程序，在数据库中生成Husband表，并在控制台输出建表语句。

Husband表中有id、name、wifeName、wifeAge属性。