关系映射是指对象之间的关系，并不是指数据库的关系，关系映射是解决当对象处于以下关系之一时，数据库表该如何映射的问题
(一)一对一单向外键关联
1、注解方式配置
创建一个Husband类和Wife类
Husband类:(getWife方法上加注解OneToOne)
package cn.orlion.hibernate.model;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.OneToOne;@Entitypublic class Husband { private int id; private String name; private Wife wife; @Id @GeneratedValue 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; } @OneToOne @JoinColumn(name="wifeId")//默认生成的外键id是wife_id在这里使用JoinColumn注解name属性指定为wifeId public Wife getWife() { return wife; } public void setWife(Wife wife) { this.wife = wife; }} Wife类
package cn.orlion.hibernate.model;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;@Entitypublic class Wife { private int id; private String name; @Id @GeneratedValue 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; }} 然后创建一个测试类HibernateMappingTest
package cn.orlion.hibernate.model;import org.hibernate.cfg.AnnotationConfiguration;import org.hibernate.tool.hbm2ddl.SchemaExport;import org.junit.Test;public class HibernateORMappingTest { @Test public void testSchemaExport(){ new SchemaExport(new AnnotationConfiguration().configure()).create(true , true); }} 运行testSchemaExport可以在控制台看到建表语句:
2、xml方式配置
首先创建一个Student类和StuIdCard(学生证)
Student类：
package cn.orlion.hibernate.model;public class Student { private int id; private String name; private String sex; 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 getSex() { return sex; } public void setSex(String sex) { this.sex = sex; }} StuIdCard：
package cn.orlion.hibernate.model;public class StuIdCard { private int id; private int num; 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; }} 然后创建两个配置文件Student.hbm.xml：
StuIdCard.hbm.xml：
然后运行测试类HibernateORMappingTest类的testSchemaExport方法可以在控制台看到建表语句:
(二)一对一双向外键关联
1、注解方式设置
双向外键关联注解方式设置是在wife类中添加husband属性，在getHusband()方法上添加注解@OneToOne(mappedBy="wife")//mappedBy="wife"表示Husband中wife属性已经做映射了，不用管当前类的设置（不再从wife表中生成指向husband的外键）注:如果不写mappedBy="wife"会在wife表中生成一个husband_id外键，这是多余的。
Wife类：
package cn.orlion.hibernate.model;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.OneToOne;@Entitypublic class Wife { private int id; private String name; private Husband husband; @Id @GeneratedValue 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; } @OneToOne(mappedBy="wife")//mappedBy="wife"表示Husband中wife属性已经做映射了，不用管当前类的设置（不再从wife表中生成指向husband的外键） public Husband getHusband() { return husband; } public void setHusband(Husband husband) { this.husband = husband; } } 2、xml方式配置
在Student.hbm.xml配置文件中添加<one-to-one name="stuIdCard" property-ref="student"></one-to-one>，在Student类中添加stuIdCard属性：Student类：
package cn.orlion.hibernate.model;public class Student { private int id; private String name; private String sex; private StuIdCard stuIdCard; 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 getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } public StuIdCard getStuIdCard() { return stuIdCard; } public void setStuIdCard(StuIdCard stuIdCard) { this.stuIdCard = stuIdCard; } } Student.hbm.xml:
注：一对一单向和双向在数据库中表现没有区别
主键关联是指的一个表的主键和另外一个表的主键关联
外键关联是指的一个表的主键和另外一个表的非主键关联
（三）一对一单向主键关联
xml方式配置：
创建Student类
package cn.orlion.hibernate.model;public class Student { private int id; private String name; private String sex; 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 getSex() { return sex; } public void setSex(String sex) { this.sex = sex; }} StuIdCard类：
package cn.orlion.hibernate.model;public class StuIdCard { private int id; private int num; 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; }} Student.hbm.xml:
StuIdCard.hbm.xml:
student
运行：
（四）一对一双向主键关联
注解方式配置:
Husband类：
package cn.orlion.hibernate.model;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.OneToOne;import javax.persistence.PrimaryKeyJoinColumn;@Entitypublic class Husband { private int id; private String name; private Wife wife; @Id @GeneratedValue 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; } @OneToOne @PrimaryKeyJoinColumn public Wife getWife() { return wife; } public void setWife(Wife wife) { this.wife = wife; }}
Wife类：
package cn.orlion.hibernate.model;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.OneToOne;@Entitypublic class Wife { private int id; private String name; private Husband husband; @Id @GeneratedValue 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; } @OneToOne @PrimaryKeyJoinColumn public Husband getHusband() { return husband; } public void setHusband(Husband husband) { this.husband = husband; } }
（五）联合主键映射
Wife类：
package cn.orlion.hibernate.model;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.IdClass;@Entity@IdClass(WifePK.class)public class Wife { private int id; private String name; private String age; @Id public int getId() { return id; } public void setId(int id) { this.id = id; } @Id public String getName() { return name; } public void setName(String name) { this.name = name; } public String getAge() { return age; } public void setAge(String age) { this.age = age; } } WifePK：
package cn.orlion.hibernate.model;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; }} Husband类：
package cn.orlion.hibernate.model;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.JoinColumns;import javax.persistence.OneToOne;@Entitypublic class Husband { private int id; private String name; private Wife wife; @Id @GeneratedValue 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; } @OneToOne @JoinColumns( { @JoinColumn(name="wifeId" , referencedColumnName="id"), @JoinColumn(name="wifeName" , referencedColumnName="name") } ) public Wife getWife() { return wife; } public void setWife(Wife wife) { this.wife = wife; }} 运行结果：
