hibernate 7种映射关系

1.一对多单向
类结构：一端持有多段的集合，多端持有一端的对象
表结构：多段持有一端的外键（即使是存在于心中的外键）
Department

public class Department {    private int id;    private String name;    private Set<Employee> employeeSet;    ...}

Employee

public class Employee {    private int id;    private String name;    ...}

Department.hbm.xml

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping>    <class name="com.test.relationship.model.Department" table="t_department">        <id name="id" type="int">            <column name="d_id" />            <generator class="native" />        </id>        <property name="name" type="java.lang.String">            <column name="d_name" />        </property>        <!-- set标签：集合             name：集合的属性名称             table：集合对应的表 -->        <set name="employeeSet" table="t_employee">            <!-- key标签：外键关联 -->            <key>                <!-- column：外键字段 -->                <column name="e_d_id" />            </key>            <!-- 映射关系                 class：集合对应的类的全名 -->            <one-to-many class="com.test.relationship.model.Employee" />        </set>    </class></hibernate-mapping>

Employee.hbm.xml

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping>    <class name="com.test.relationship.model.Employee" table="t_employee">        <id name="id" type="int">            <column name="e_id" />            <generator class="native" />        </id>        <property name="name" type="java.lang.String">            <column name="e_name" />        </property>    </class></hibernate-mapping>

测试代码

@Test    public void testAdd() {        Employee e1 = new Employee("zs");        Employee e2 = new Employee("ls");        Set<Employee> employeeSet = new HashSet<Employee>();        employeeSet.add(e1);        employeeSet.add(e2);        Department d = new Department("市场部");        d.setEmployeeSet(employeeSet);        session.save(e1);        session.save(e2);        session.save(d);    }

说明：与插入顺序无关，始终先插入多端，再插入一端，再更新多端

2.多对一单向
Department

public class Department {    private int id;    private String name;    ...}

Employee

public class Employee {    private int id;    private String name;    private Department department;    ...}

Department.hbm.xml中去掉set
Employee.hbm.xml中增加

<many-to-one name="department" class="com.test.relationship.model.Department">            <column name="e_d_id" /></many-to-one>

说明：优先插入一端，可以执行较少sql语句

3.一对多双向
把上面的两个合在一起就是一对多双向

4.一对一单向
有主键关联和唯一外键关联，这里仅展示唯一外键关联，可以理解为一对多的特例
Card

public class Card {    private String id;    ...}

Person

public class Person {    private String id;    private String name;    private Card card;    ...}

Person.hbm.xml

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping>    <class name="com.test.hibernate.model.Person" table="t_person">        <id name="id" type="java.lang.String">            <column name="p_id" />            <generator class="assigned" />        </id>        <property name="name" type="java.lang.String">            <column name="p_name" />        </property>        <!-- 添加unique作为限制 -->        <many-to-one name="card" class="com.test.hibernate.model.Card" fetch="join"  unique="true">            <column name="p_c_id" />        </many-to-one>    </class></hibernate-mapping>

5.一对一双向
Card

public class Card {    private String id;    private Person person;    ...}

Person

public class Person {    private String id;    private String name;    private Card card;    ...}

Card.hbm.xml

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping>    <class name="com.test.hibernate.model.Card" table="t_card">        <id name="id" type="java.lang.String">            <column name="c_id" />            <generator class="assigned" />        </id>        <!-- name：属性             class：对应的类的全名             property-ref：关联的属性 -->        <one-to-one name="person" class="com.test.hibernate.model.Person" property-ref="card" fetch="join"></one-to-one>    </class></hibernate-mapping>

6.多对多单向
Course

public class Course {    private int id;    private String name;    ...}

Student

public class Student {    private int id;    private String name;    private Set<Course> set;    ...}

Student.hbm.xml

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping>    <class name="com.test.hibernate.model.Student" table="t_student">        <id name="id" type="int">            <column name="s_id" />            <generator class="native" />        </id>        <property name="name" type="java.lang.String">            <column name="s_name" />        </property>        <!-- table：中间表 -->        <set name="set" table="t_student_course" inverse="false" lazy="true">            <!-- 外键关联的字段 -->            <key>                <column name="s_id" />            </key>            <!-- 映射关系                 class：另外一张表的对象的类全名                 column：中间表外键关联另外一张表的字段 -->            <many-to-many class="com.test.hibernate.model.Course" column="c_id"/>        </set>    </class></hibernate-mapping>

7.多对多双向
Course

public class Course {    private int id;    private String name;    private Set<Student> set;    ...}

Student

public class Student {    private int id;    private String name;    private Set<Course> set;    ...}

Course.hbm.xml

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping>    <class name="com.test.hibernate.model.Course" table="t_course">        <id name="id" type="int">            <column name="c_id" />            <generator class="native" />        </id>        <property name="name" type="java.lang.String">            <column name="c_name" />        </property>        <set name="set" table="t_student_course">            <key>                <column name="c_id" />            </key>            <many-to-many class="com.test.hibernate.model.Student" column="s_id"/>        </set>    </class></hibernate-mapping>