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03_Hibernate关系映射

关系映射？

Hibernate的主要目的就是JAVA程序员可以随心所欲的使用对象编程思维来操作数据库。一些数据库表的关系我们应该可以通过hibernate实现，比如数据库中用到的主外键关系，还有一些与主外键关系的设置，比如主键的信息被删除，外键关联的信息也要删除等，所以hibernate同样应该实现这种映射关系。

系统设计中的三种实体关系

数据库实体表之间的关系映射

一对多：客户(customers)和订单(orders)的关系

一般在多的一方添加外键

一对一：公司(company)和公司地址(address)的关系

在任意一方添加对方的主键作为外键

多对多：订单(orders)和商品(products)数据表

关系上升为第三张表，分别引入双方的主键作为外键

Hibernate关联映射

hibernate的一对多关联映射又分为两种实现方式：

单项关联：立从employee到department的多对一关联，或者仅仅建立从department到employee的一对多关联。

双项关联：既建立从employee到department的多对一关联，又建立从department到employee的一对多关联。

1.单向多对一

员工emp和部门dept，

规则：在多的一方配置,多的一方要封装一个(一的一方)属性
name:是一的一方的属性名 , column:外键列名 class:one的类的全路径
<many-to-one name="dept" column="deptid" class="com.manytoone.Dept" not-null="false" cascade="all">
</many-to-one>

Emp.java

public class Emp {
    private Integer eid;
    private String ename;
    private Dept dept;

    public Integer getEid() {
        return eid;
    }

    public void setEid(Integer eid) {
        this.eid = eid;
    }

    public String getEname() {
        return ename;
    }

    public void setEname(String ename) {
        this.ename = ename;
    }

    public Dept getDept() {
        return dept;
    }

    public void setDept(Dept dept) {
        this.dept = dept;
    }
}

Emp.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!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.manytoone.Emp" table="emp">
    <id name="eid" column="eid" type="java.lang.Integer" length="10">
        <!--主键生成策略-->
        <generator class="increment">
        </generator>
    </id>
    <!--ename属性-->
    <property name="ename" column="ename" type="java.lang.String" length="50">
    </property>
    <!--name:属性名  column:外键  class: 与name属性的全路径  cascade:表示会影响所关联的的表-->
    <many-to-one name="dept" column="deptid" class="com.manytoone.Dept" not-null="false" cascade="save-update">
    </many-to-one>
</class>
</hibernate-mapping>

Dept.java

public class Dept {
    private Integer did;
    private String dname;

    public Integer getDid() {
        return did;
    }

    public void setDid(Integer did) {
        this.did = did;
    }

    public String getDname() {
        return dname;
    }

    public void setDname(String dname) {
        this.dname = dname;
    }
}

dept.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!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.manytoone.Dept" table="dept">
    <id name="did" column="did" type="java.lang.Integer" length="10">
        <!--主键生成策略-->
        <generator class="increment">
        </generator>
    </id>
    <!--dname属性-->
    <property name="dname" column="dname" type="java.lang.String" length="50">
    </property>
</class>
</hibernate-mapping>

2.单向一对多关联

dept->emp(单向一对多)

规则：在一的一方配置,要封装一个set集合.

<set name="emps" table="emp" cascade="all">
   <key>
           
       <column name="deptid"></column>
   </key>
   
   <one-to-many class="Emp"/>
</set>

dept.java

public class Dept {
    private Integer did;
    private String dname;
    private Set<Emp> emps = new HashSet<Emp>();

    public Integer getDid() {
        return did;
    }

    public void setDid(Integer did) {
        this.did = did;
    }

    public String getDname() {
        return dname;
    }

    public void setDname(String dname) {
        this.dname = dname;
    }

    public Set<Emp> getEmps() {
        return emps;
    }

    public void setEmps(Set<Emp> emps) {
        this.emps = emps;
    }
}

Dept.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!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.onetomany.Dept" table="dept" lazy="true">
    <id name="did" column="did" type="java.lang.Integer" length="10">
        <!--主键生成策略-->
        <generator class="increment">
        </generator>
    </id>
    <!--dname属性-->
    <property name="dname" column="dname" type="java.lang.String" length="50">
    </property>
    <!--关联级别及时加载，查询时会把关联的也会查询出来-->
    <set name="emps" table="emp" cascade="all" lazy="true">
        <key>
            <column name="deptid"></column> <!--外键-->
        </key>
        <one-to-many class="com.onetomany.Emp"/><!--外键关联的类-->
    </set>
</class>
</hibernate-mapping>

Emp.java


public class Emp {
    private Integer eid;
    private String ename;
    private Integer deptid;

    public Integer getEid() {
        return eid;
    }

    public void setEid(Integer eid) {
        this.eid = eid;
    }

    public String getEname() {
        return ename;
    }

    public void setEname(String ename) {
        this.ename = ename;
    }

    public Integer getDeptid() {
        return deptid;
    }

    public void setDeptid(Integer deptid) {
        this.deptid = deptid;
    }
}

Emp.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!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.onetomany.Emp" table="emp">
    <id name="eid" column="eid" type="java.lang.Integer" length="10">
        <!--主键生成策略-->
        <generator class="increment">
        </generator>
    </id>
    <!--ename属性-->
    <property name="ename" column="ename" type="java.lang.String" length="50">
    </property>
    <property name="deptid" column="deptid" type="java.lang.Integer" length="10">
    </property>
</class>
</hibernate-mapping>

3.双向一对多*

dept->Emp

规则：1.在多的一方配置,多的一方要封装一个(一的一方)属性
2.在一的一方配置,要封装一个set集合.
上述两个配置综合

Dept.java

public class Dept {
    private Integer did;
    private String dname;
    private Set<Emp> emps = new HashSet<Emp>();

    public Integer getDid() {
        return did;
    }

    public void setDid(Integer did) {
        this.did = did;
    }

    public String getDname() {
        return dname;
    }

    public void setDname(String dname) {
        this.dname = dname;
    }

    public Set<Emp> getEmps() {
        return emps;
    }

    public void setEmps(Set<Emp> emps) {
        this.emps = emps;
    }
}

Dept.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!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.doubleonetomany.Dept" table="dept">
        <id name="did" column="did" type="java.lang.Integer" length="10">
            <!--主键生成策略-->
            <generator class="increment">
            </generator>
        </id>
        <!--dname属性-->
        <property name="dname" column="dname" type="java.lang.String" length="50">
        </property>
        <set name="emps" table="emp" cascade="all">
            <key>
                <column name="deptid"></column> <!--外键-->
            </key>
            <one-to-many class="com.doubleonetomany.Emp"/><!--外键关联的类-->

        </set>
    </class>
</hibernate-mapping>

Emp.java

public class Emp {
    private Integer eid;
    private String ename;
    private Dept dept;

    public Integer getEid() {
        return eid;
    }

    public void setEid(Integer eid) {
        this.eid = eid;
    }

    public String getEname() {
        return ename;
    }

    public void setEname(String ename) {
        this.ename = ename;
    }

    public Dept getDept() {
        return dept;
    }

    public void setDept(Dept dept) {
        this.dept = dept;
    }
}

Emp.hbn.xml

<?xml version="1.0" encoding="UTF-8"?>
<!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.icss.doubleonetomany.Emp" table="emp">
    <id name="eid" column="eid" type="java.lang.Integer" length="10">
        <!--主键生成策略-->
        <generator class="increment">
        </generator>
    </id>
    <!--ename属性-->
    <property name="ename" column="ename" type="java.lang.String" length="50">
    </property>
    <!--name:属性名  column:外键  class: 与name属性的全路径  cascade:表示会影响所关联的的表-->
    <many-to-one name="dept" column="deptid" class="com.icss.doubleonetomany.Dept" not-null="false">
    </many-to-one>
</class>
</hibernate-mapping>

4.双向一对一

employee->joinpart 员工和入党申请书

规则：在实体类中分别要定义对方类型的属性
在有外键一方配置：<many-to-one name="joinpart" column="joinpart_id" class="JoinPart" cascade="save-update"></many-to-one>
在没有外键的一方配置：<one-to-one name="emp" class="Employee" property-ref="joinpart"></one-to-one>
注：property-ref：对方封装的相关类型的属性

Employee.java

package com.icss.doubleonetoone;

import java.util.Date;

/**
 * Created by jiatp on 2019/8/2.
 */
public class Employee {
    private Integer eid;
    private String name;
    private Date birthday;
    private JoinPart joinPart;

    public JoinPart getJoinPart() {
        return joinPart;
    }

    public void setJoinPart(JoinPart joinPart) {
        this.joinPart = joinPart;
    }

    public Integer getEid() {
        return eid;
    }

    public void setEid(Integer eid) {
        this.eid = eid;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }
}

Employee.hbm.java

<?xml version="1.0" encoding="UTF-8"?>
<!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.doubleonetoone.Employee" table="employee">
        <id name="eid" column="eid" type="java.lang.Integer" length="10">
            <generator class="increment"/>
        </id>
        <property name="name" column="name" type="java.lang.String" length="50">
        </property>
        <property name="birthday" column="birthday" type="java.util.Date">
        </property>
        <many-to-one name="joinPart" column="joinPart_id" class="com.doubleonetoone.JoinPart" cascade="save-update"></many-to-one>
    </class>
</hibernate-mapping>

JoinPart.java

public class JoinPart {
    private Integer jid;
    private Date joindate;
    private Employee emp;

    public Integer getJid() {
        return jid;
    }

    public void setJid(Integer jid) {
        this.jid = jid;
    }

    public Date getJoindate() {
        return joindate;
    }

    public void setJoindate(Date joindate) {
        this.joindate = joindate;
    }

    public Employee getEmp() {
        return emp;
    }

    public void setEmp(Employee emp) {
        this.emp = emp;
    }
}

JoinPart.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!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.icss.doubleonetoone.JoinPart" table="joinPart">
        <id name="jid" column="jid" type="java.lang.Integer" length="10">
            <generator class="increment"/>
        </id>
        <property name="joindate" column="joindate" type="java.util.Date">
        </property>
        <one-to-one name="emp" class="com.doubleonetoone.Employee" property-ref="joinPart"></one-to-one>
    </class>
</hibernate-mapping>

5.双向多对多

User->Role 用户和角色

规则：双向多对多
处理中间表,在中间表中存放它们的外键
name：集合类型的属性名 table：中间表的表名 column: 中间与之对应的外键
class : 后面many方的类的全路径 column: 后面many类对应中间表的外键
<set name="users" table="sys_role_user">
<key column="r_id"></key>
<many-to-many class="User" column="u_id"></many-to-many>
</set>

User.java

public class User {
    private Integer uid;
    private String name;
    private Set<Role> roles = new HashSet<Role>(); //双向多对多

    public Integer getUid() {
        return uid;
    }

    public void setUid(Integer uid) {
        this.uid = uid;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Set<Role> getRoles() {
        return roles;
    }

    public void setRoles(Set<Role> roles) {
        this.roles = roles;
    }
}

User.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!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.doublemanytomany.User" table="user">
        <id name="uid" column="uid" type="java.lang.Integer" length="10">
            <!--主键生成策略-->
            <generator class="increment">
            </generator>
        </id>
        <property name="name" column="name" length="50" type="java.lang.String">
        </property>
        <!--inverses属性;true关联维护时将控制权交给对方-->
        <set name="roles" table="sys_role_user" inverse="true">
            <key column="u_id">
            </key>
            <many-to-many class="com.doublemanytomany.Role" column="r_id">
            </many-to-many>
        </set>
       
    </class>
</hibernate-mapping>

Role.java

public class Role {
    private Integer rid;
    private String name;
    private Set<User> users = new HashSet<User>();  //多对多

    public Integer getRid() {
        return rid;
    }

    public void setRid(Integer rid) {
        this.rid = rid;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Set<User> getUsers() {
        return users;
    }

    public void setUsers(Set<User> users) {
        this.users = users;
    }
}

Role.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!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.doublemanytomany.Role" table="role">
        <id name="rid" column="rid" type="java.lang.Integer" length="10">
            <!--主键生成策略-->
            <generator class="increment">
            </generator>
        </id>
        <property name="name" type="java.lang.String" column="name" length="50">
        </property>
        <set name="users" table="sys_role_user">
            <key column="r_id">
            </key>
            <many-to-many class="com.doublemanytomany.User" column="u_id">
            </many-to-many>
        </set>

    </class>
</hibernate-mapping>

注意：对于双向 n-n 关联, 须把其中一端的 inverse 设置为 true, 否则可能会造成主键冲突.

测试

/**
 * Description:测试双向多对多关联
 * User:jiatp
 * Date: 2019/8/3 18:14
 */
public class doublemanytomanyTest {
    @Test
    public void test(){
        Session session = HibernateUtils.openSession();
        Transaction ts = session.beginTransaction();
        //创建用户
        User user1 = new User();
        user1.setName("jtp");

        // 创建角色
        Role role = new Role();
        role.setName("CEO");

        //关联关系
        user1.getRoles().add(role);
        role.getUsers().add(user1);
        session.save(user1);
        session.save(role);


        ts.commit();
        session.close();

    }
}

只举例双向对多的例子，其余的自行测试。

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原文地址：https://www.cnblogs.com/jatpeo/p/11767538.html