Hibernate的单向关联映射应用

一、简述

一、单向N-1关联单向N-1关系，比如多个人对应一个地址，只需从人实体端可以找到对应的地址实体，无须关系某个地址的全部住户。单向 n-1 关联只需从 n 的一端可以访问 1 的一端。二、单向1-1关联从持久化的代码上看，单向1-1与单向N-1没有丝毫区别。三、N-N关系持久化类里需要使用集合属性，此时集合里的元素是关联实体

二、简单例子
1、数据库表

person表：CREATE TABLE `person` (  `personId` int(50) NOT NULL AUTO_INCREMENT,  `personName` varchar(50) COLLATE utf8_unicode_ci DEFAULT NULL,  `personAge` int(50) DEFAULT NULL,  `addressId` int(11) DEFAULT NULL,  PRIMARY KEY (`personId`)) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ciaddress表：CREATE TABLE `address` (  `addressId` int(50) NOT NULL AUTO_INCREMENT,  `addressDetail` varchar(100) COLLATE utf8_unicode_ci DEFAULT NULL,  PRIMARY KEY (`addressId`)) ENGINE=InnoDB AUTO_INCREMENT=13 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ciperson_address表：CREATE TABLE `person_address` (  `addressId` int(50) NOT NULL AUTO_INCREMENT,  `personId` int(50) DEFAULT NULL,  PRIMARY KEY (`addressId`)) ENGINE=InnoDB AUTO_INCREMENT=13 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci

2、实体

package com;import java.util.HashSet;import java.util.Set;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.JoinTable;import javax.persistence.ManyToMany;import javax.persistence.Table;import org.hibernate.annotations.Cascade;@Entity@Table(name="person")public class Person {    @Id    @Column(name="personId")    @GeneratedValue(strategy=GenerationType.IDENTITY)    private Integer personId;    @Column(name="personName")    private String personName;    @Column(name="personAge")    private Integer personAge;    //----------------单向N-1关联Begin-------------//    //========无连接表(中间表)的N-1关联===========//    //  //定义该Person实体关联的Address实体    //  @ManyToOne(targetEntity=Address.class)    //  //映射外键列，指定外键列的列名为addressId    //  @JoinColumn(name="addressId",nullable=false)    //  @Cascade(CascadeType.ALL)    //========有连接表(中间表)的N-1关系============//    //定义该Person实体关联的Address实体    //  @ManyToOne(targetEntity=Address.class)    //  //显式使用@joinTable映射连接表    //  @JoinTable(name="person_address",//指定连接表的表名为person_address    //  //指定连接表中personId外键列，参考当前 实体对应表的主键列    //  joinColumns=@JoinColumn(name="personId",referencedColumnName="personId",unique=true),    //  //指定连接表中addressId外键列，参照当前实体 关联实体 对应表的主键列    //  inverseJoinColumns=@JoinColumn(name="addressId",referencedColumnName="addressId")    //  )    //  @Cascade(CascadeType.ALL)    //-----------------单向N-1关联END----------------//    //-----------------单向1-1关联Begin------------------//    //==================基于外键的单向1-1关联===============//    //定义该person实体关联的Address实体    //  @OneToOne(targetEntity=Address.class)    //  //映射名为addressId的外键列，参照关联实体对应表addressId主键列    //  @JoinColumn(name="addressId",    //  //指定连接表中addressId外键列，参照当前实体关联实体对应表的主键列      //  referencedColumnName="addressId",unique=true)    //  @Cascade(CascadeType.ALL)    //===================有连接表(中间表)的1-1关联============//    //  @OneToOne(targetEntity=Address.class)    //  @JoinTable(name="person_address",//指定连接表的表名为person_address    //    //用于配置连接表中外键列信息，这些外键列参照当前实体对应表的主键列    //  joinColumns=@JoinColumn(name="personId",referencedColumnName="personId",unique=true),    //  //用于配置连接表中外键列信息，这些外键列参照当前实体关联实体对应的主键列    //  inverseJoinColumns=@JoinColumn(name="addressId",referencedColumnName="addressId",unique=true)    //  )    //  @Cascade(CascadeType.ALL)    //=====================单向1-1关联End==================//    //=====================单向N-N关联=====================//    //定义该Person实体所有关联的Address实体    @ManyToMany(targetEntity=Address.class)    //映射链接表为person_address    @JoinTable(name="person_address",    //定义连接表中名为person_id的外键列，该外键参照当前实体对应的主键列    joinColumns=@JoinColumn(name="personId",referencedColumnName="personId"),    //定义连接表中名为address_id的外键列，该外键列参照当前实体关联实体对应表的主键列，没有指定unique=true    inverseJoinColumns=@JoinColumn(name="addressId",referencedColumnName="addressId")    )    @Cascade(org.hibernate.annotations.CascadeType.ALL)    //======================单向N-N关联End====================//    private Set<Address> addresses=new HashSet();    /**      *        * //  private Address address;        //  public Address getAddress() {        //      return address;        //  }        //  public void setAddress(Address address) {        //      this.address = address;        //  }     *      * @return     */    public Integer getPersonId() {        return personId;    }    public void setPersonId(Integer personId) {        this.personId = personId;    }    @Column(name="personName")    public String getPersonName() {        return personName;    }    public void setPersonName(String personName) {        this.personName = personName;    }    @Column(name="personAge")    public Integer getPersonAge() {        return personAge;    }    public void setPersonAge(Integer personAge) {        this.personAge = personAge;    }    public Set<Address> getAddresses() {        return addresses;    }    public void setAddresses(Set<Address> addresses) {        this.addresses = addresses;    }}package com;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.Table;@Entity@Table(name="address")public class Address {    @Id     @Column(name="addressId")    @GeneratedValue(strategy=GenerationType.IDENTITY)     private Integer addressId;    private String addressDetail;    public Address(){    }    public Address(String addressDetail){        this.addressDetail=addressDetail;    }    public Integer getAddressId() {        return addressId;    }    public void setAddressId(Integer addressId) {        this.addressId = addressId;    }    @Column(name="addressDetail")    public String getAddressDetail() {        return addressDetail;    }    public void setAddressDetail(String addressDetail) {        this.addressDetail = addressDetail;    }}

3、测试类

package com;import java.util.HashSet;import java.util.Set;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.Transaction;import org.hibernate.cfg.Configuration;public class TestPerson {    public static void main(String[] args) {        Configuration config=new Configuration().configure();        SessionFactory sfy=config.buildSessionFactory();        Session session=sfy.openSession();        Transaction tx=session.beginTransaction();        Person p=new Person();        Address a=new Address("茂名市茂南区N_N有连接表");        p.setPersonName("person_N_N有连接关联");        p.setPersonAge(25);        // p.setAddress(a);        //持久化person对象        session.persist(p);        Address a2=new Address("茂名市化州市N_N有连接关联");        //修改持久状态的p2        //p.setAddress(a2);        Set<Address> addresses=new HashSet<Address>();        addresses.add(a);        addresses.add(a2);        p.setAddresses(addresses);        tx.commit();        session.close();        sfy.close();    }}