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;

@Entity

public 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;

@Entity

public 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：

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="cn.orlion.hibernate.model">

    <class name="cn.orlion.hibernate.model.Student">

        <id name="id">

            <generator class="native"></generator>

        </id>

        <property name="name"></property>

        <property name="sex"></property>

    </class>

</hibernate-mapping>

StuIdCard.hbm.xml：

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="cn.orlion.hibernate.model">

    <class name="cn.orlion.hibernate.model.StuIdCard">

        <id name="id">

            <generator class="native"></generator>

        </id>

        <property name="num" />

        <many-to-one name="student" column="studentId" unique="true"></many-to-one>

        <!-- many-to-one是当前类即StuIdCard类相对于Student类是多对一关系 （多个学生证对应一个学生） ，unique=true限定为了一对一 -->

    </class>

</hibernate-mapping>

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;

@Entity

public 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:

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="cn.orlion.hibernate.model">

    <class name="cn.orlion.hibernate.model.Student">

        <id name="id">

            <generator class="native"></generator>

        </id>

        <property name="name"></property>

        <property name="sex"></property>

        <one-to-one name="stuIdCard" property-ref="student"></one-to-one>

        <!-- one-to-one只会在一边生成主键，如果这里设置为many-to-one会在student表中生成多余的stuidcard_id外键 -->

        <!-- property-ref="student" 类似于mappedby="student"是指在StuIdCard中student属性已经设置好了关联关系 -->

    </class>

</hibernate-mapping>

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:

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="cn.orlion.hibernate.model">

    <class name="cn.orlion.hibernate.model.Student">

        <id name="id">

            <generator class="native"></generator>

        </id>

        <property name="name"></property>

        <property name="sex"></property>

    </class>

</hibernate-mapping>

StuIdCard.hbm.xml:

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="cn.orlion.hibernate.model">

    <class name="cn.orlion.hibernate.model.StuIdCard">

        <id name="id">

            <generator class="foreign"><!-- StuIdCard的主键应该靠外键来生成，StuIdCard -->

                <param name="property">student</param><!-- 依靠student属性的关联关系 -->

            </generator>

        </id>

        <property name="num" />

        <one-to-one name="student" constrained="true"></one-to-one>

        <!-- constrained="true"用来生成外键约束，不加这个属性就不会加外键 -->

    </class>

</hibernate-mapping>

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;

@Entity

public 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;

@Entity

public 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;

@Entity

public 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：

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