03_Hibernate关系映射

谁践踏了优雅 2024-04-17 05:41 73阅读 0赞

**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**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2phdHBlbg_size_16_color_FFFFFF_t_70][]

**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">
            
            <generator class="increment">
            </generator>
        </id>
        
        <property name="ename" column="ename" type="java.lang.String" length="50">
        </property>
        
        <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

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">
            
            <generator class="increment">
            </generator>
        </id>
        
        <property name="dname" column="dname" type="java.lang.String" length="50">
        </property>
        
        <set name="emps" table="emp" cascade="all" lazy="true">
            <key>
                <column name="deptid"></column> 
            </key>
            <one-to-many class="com.onetomany.Emp"/>
        </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">
            
            <generator class="increment">
            </generator>
        </id>
        
        <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

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">
                
                <generator class="increment">
                </generator>
            </id>
            
            <property name="dname" column="dname" type="java.lang.String" length="50">
            </property>
            <set name="emps" table="emp" cascade="all">
                <key>
                    <column name="deptid"></column> 
                </key>
                <one-to-many class="com.doubleonetomany.Emp"/>
    
            </set>
        </class>
    </hibernate-mapping>

Emp.java

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">
            
            <generator class="increment">
            </generator>
        </id>
        
        <property name="ename" column="ename" type="java.lang.String" length="50">
        </property>
        
        <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

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">
                
                <generator class="increment">
                </generator>
            </id>
            <property name="name" column="name" length="50" type="java.lang.String">
            </property>
            
            <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">
                
                <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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