Hibernate 1-N单向关联（注解实现）

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无连接表的1-N单向关联

Person.java（1端）

package com.oneToMany;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.OneToMany;import javax.persistence.Table;@Entity@Table(name="person_inf")public class Person {    @Id    @Column(name="person_id")//name="person_id"    @GeneratedValue(strategy=GenerationType.IDENTITY)    private Integer id;    private String name;    private int age;    @OneToMany(targetEntity=Address.class)    //映射外键列，此处映射的外键列会添加到关联实体对应的数据库中    @JoinColumn(name="fk_person_id" ,referencedColumnName="person_id")//name="fk_person_id" ,referencedColumnName="person_id"    //N的一端以集合set形式出现    private Set<Address> address=new HashSet<Address>();    public Integer getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public Set<Address> getAddress() {        return address;    }    public void setAddress(Set<Address> address) {        this.address = address;    }}

Address.java（N端）

package com.oneToMany;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_inf")//catalog="hibernate_oneToMany",name="address_inf"public class Address {    @Id    @Column(name="address_id")//name="address_id"    @GeneratedValue(strategy=GenerationType.IDENTITY)    private Integer id;    private String addressDetail;    public Address(){}    public Address(String addressDetail ){        this.addressDetail=addressDetail;                }    public void setId(Integer id) {        this.id = id;    }    public Integer getId() {        return id;    }    public void setAddressDetail(String addressDetail) {        this.addressDetail = addressDetail;    }    public String getAddressDetail() {        return addressDetail;    }}

TestDemo.java

public static void test2() {        StandardServiceRegistry registry = new StandardServiceRegistryBuilder()                .configure("hibernate.cfg.xml").build();        SessionFactory factory = new MetadataSources(registry).buildMetadata()                .buildSessionFactory();        // 获取Session        Session session = factory.openSession();        Transaction transaction = session.beginTransaction();        try {            Person person = new Person();            // 持久化Person对象            session.save(person);            Address address = new Address("GDUT");            person.setName("Jeff");            person.setAge(21);            // 持久化Address对象            session.persist(address);            // 添加地址1            person.getAddress().add(address);            Address address2 = new Address("SCGT");            // 添加地址2            person.getAddress().add(address2);            // 持久化Address对象            session.persist(address2);            transaction.commit();        } catch (Exception e) {            transaction.rollback();// 回滚事务            e.getMessage();        } finally {            if (session != null) {                session.close();            }        }    }```![效果图片](http://img.blog.csdn.net/20160901225532760)----------**有连接表的1-N单向关联**----------Person.java<div class="se-preview-section-delimiter"></div>

package com.oneToMany;

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.OneToMany;
import javax.persistence.Table;

@Entity
@Table(name=”person_inf”)
public class Person {

@Id@Column(name="person_id")//name="person_id"@GeneratedValue(strategy=GenerationType.IDENTITY)private Integer id;private String name;private int age;@OneToMany(targetEntity=Address.class)/* * @JoinTable(name="person_address", * //定义连接表中名为fk_person_id的外键列，该外键列参照当前实体对应的主键列 * joinColumns=@JoinColumn(name="fk_person_id" * ,referencedColumnName="person_id"), * //定义连接表中名为fk_address_id的外键列，该外键列参照当前实体关联实体对应的主键列 * inverseJoinColumns=@JoinColumn * (name="fk_address_id",referencedColumnName="address_id", unique=true)) * * @JoinTable注解映射fk_address_id外键列，添加了唯一约束，说明一个Address实体至多只能关联一个 * Person实体，而一个Person实体可以关联多个Address实体 *  */@JoinTable(name="person_address",        //定义连接表中名为fk_person_id的外键列，该外键列参照当前实体对应的主键列joinColumns=@JoinColumn(name="fk_person_id",referencedColumnName="person_id"),        //定义连接表中名为fk_address_id的外键列，该外键列参照当前实体关联实体对应的主键列inverseJoinColumns=@JoinColumn(name="fk_address_id",referencedColumnName="address_id",unique=true))//N的一端以集合set形式出现private Set<Address> address=new HashSet<Address>();public Integer getId() {    return id;}public void setId(Integer id) {    this.id = id;}public String getName() {    return name;}public void setName(String name) {    this.name = name;}public int getAge() {    return age;}public void setAge(int age) {    this.age = age;}public Set<Address> getAddress() {    return address;}public void setAddress(Set<Address> address) {    this.address = address;}

}

Address.java<div class="se-preview-section-delimiter"></div>

package com.oneToMany;

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_inf”)//catalog=”hibernate_oneToMany”,name=”address_inf”
public class Address {

@Id@Column(name="address_id")//name="address_id"@GeneratedValue(strategy=GenerationType.IDENTITY)private Integer id;private String addressDetail;public Address(){}public Address(String addressDetail ){    this.addressDetail=addressDetail;            }public void setId(Integer id) {    this.id = id;}public Integer getId() {    return id;}public void setAddressDetail(String addressDetail) {    this.addressDetail = addressDetail;}public String getAddressDetail() {    return addressDetail;}

}

TestDemo.java<div class="se-preview-section-delimiter"></div>

public static void test2() {

    StandardServiceRegistry registry = new StandardServiceRegistryBuilder()            .configure("hibernate.cfg.xml").build();    SessionFactory factory = new MetadataSources(registry).buildMetadata()            .buildSessionFactory();    // 获取Session    Session session = factory.openSession();    Transaction transaction = session.beginTransaction();    try {        Person person = new Person();        // 持久化Person对象        session.save(person);        Address address = new Address("GDUT");        person.setName("Jeff");        person.setAge(21);        // 持久化Address对象        session.persist(address);        // 添加地址1        person.getAddress().add(address);        Address address2 = new Address("SCGT");        // 添加地址2        person.getAddress().add(address2);        // 持久化Address对象        session.persist(address2);        transaction.commit();    } catch (Exception e) {        transaction.rollback();// 回滚事务        e.getMessage();    } finally {        if (session != null) {            session.close();        }    }}

“`

效果图

通过上面两个例子，我们可以知道，对于采用连接表的单向1-N关联，由于采用连接表维护了关联关系，两个对应的数据表无需增加外键列，所以两个实体对应的数据表就没有主从表关系。程序可以想先持久化哪个实体就先持久化哪个实体，不会引发性能问题。

public static void test2() {        StandardServiceRegistry registry = new StandardServiceRegistryBuilder()                .configure("hibernate.cfg.xml").build();        SessionFactory factory = new MetadataSources(registry).buildMetadata()                .buildSessionFactory();        // 获取Session        Session session = factory.openSession();        Transaction transaction = session.beginTransaction();        try {            Person person = new Person();            // 持久化Person对象            session.save(person);            Address address = new Address("GDUT");            person.setName("Jeff");            person.setAge(21);            // 持久化Address对象            session.persist(address);            // 添加地址1            person.getAddress().add(address);            Address address2 = new Address("SCGT");            // 添加地址2            person.getAddress().add(address2);            // 持久化Address对象            session.persist(address2);            transaction.commit();        } catch (Exception e) {            transaction.rollback();// 回滚事务            e.getMessage();        } finally {            if (session != null) {                session.close();            }        }    }

通过图片知道，我们可以知道，对于采用连接表的单向1-N关联，由于采用连接表维护了关联关系，两个对应的数据表无需增加外键列，所以两个实体对应的数据表就没有主从表关系。程序可以想先持久化哪个实体就先持久化哪个实体，不会引发性能问题。对于没有连接表的关联来说，要想优化性能，在持久化Address类之前，我们需要给Address实体指定关联的实体，就是person.getAddress().add(address)。

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