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Hibernate，JPA注解@ManyToMany

@ManyToMany默认处理机制，当双向多对多关联中没有定义任何物理映射时, Hibernate根据以下规则生成相应的值：

关联表名: 主表表名+_下划线+从表表名；

关联到主表的外键名：从表用于关联的属性名+_下划线+主表中的主键列名；

关联到从表的外键名：主表用于关联的属性名+_下划线+从表的主键列名，以上规则对于双向一对多关联同样有效。

用例代码如下：

数据库DDL语句

1，CAT表

 1 create table CAT
 2 (
 3   id          VARCHAR2(32 CHAR) not null,
 4   create_time TIMESTAMP(6),
 5   update_time TIMESTAMP(6),
 6   cat_name    VARCHAR2(255 CHAR),
 7   first_name  VARCHAR2(255 CHAR),
 8   last_name   VARCHAR2(255 CHAR),
 9   version     NUMBER(10) not null
10 )

2，HOBBY表

1 create table HOBBY
2 (
3   id          VARCHAR2(32 CHAR) not null,
4   create_time TIMESTAMP(6),
5   update_time TIMESTAMP(6),
6   name        VARCHAR2(255 CHAR),
7   cat_id      VARCHAR2(32 CHAR)
8 )

hibernate.cfg.xml

 1 <?xml version="1.0" encoding="utf-8" ?>
 2 <!DOCTYPE hibernate-configuration
 3  PUBLIC "-//Hibernate/Hibernate Configuration DTD//EN"
 4  "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
 5 <hibernate-configuration>
 6     <session-factory>
 7         <!-- 数据库驱动配置 -->
 8         <property name="dialect">org.hibernate.dialect.Oracle10gDialect</property>
 9         <property name="connection.driver_class">oracle.jdbc.OracleDriver</property>
10         <property name="connection.url">jdbc:oracle:thin:@127.0.0.1:1521:orcl</property>
11         <property name="connection.username">wxuatuser</property>
12         <property name="connection.password">xlh</property>
13         <property name="show_sql">true</property>
14         <!-- 自动执行DDL属性是update，不是true -->
15         <property name="hbm2ddl.auto">update</property>
16         <!-- hibernate实体类 -->
17         
18         <mapping class="b11_ManyToMany.Cat"/>
19         <mapping class="b11_ManyToMany.Hobby"/>
20         
21     </session-factory>
22 </hibernate-configuration>

java类

实体类 - 基类

package model;
import java.io.Serializable;
import java.util.Date;
import javax.persistence.Column;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.MappedSuperclass;
import org.hibernate.annotations.GenericGenerator;
/**
 * 实体类 - 基类
 */
@MappedSuperclass
public class BaseEntity implements Serializable {

    private static final long serialVersionUID = -6718838800112233445L;

    private String id;// ID
    private Date create_time;// 创建日期
    private Date update_time;// 修改日期
    @Id
    @Column(length = 32, nullable = true)
    @GeneratedValue(generator = "uuid")
    @GenericGenerator(name = "uuid", strategy = "uuid")
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    @Column(updatable = false)
    public Date getCreate_time() {
        return create_time;
    }
    public void setCreate_time(Date create_time) {
        this.create_time = create_time;
    }
    public Date getUpdate_time() {
        return update_time;
    }
    public void setUpdate_time(Date update_time) {
        this.update_time = update_time;
    }
    @Override
    public int hashCode() {
        return id == null ? System.identityHashCode(this) : id.hashCode();
    }
    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass().getPackage() != obj.getClass().getPackage()) {
            return false;
        }
        final BaseEntity other = (BaseEntity) obj;
        if (id == null) {
            if (other.getId() != null) {
                return false;
            }
        } else if (!id.equals(other.getId())) {
            return false;
        }
        return true;
    }
}

实体类

Cat.java

 1 package b11_ManyToMany;
 2 
 3 import java.util.Set;
 4 import javax.persistence.AttributeOverride;
 5 import javax.persistence.AttributeOverrides;
 6 import javax.persistence.Column;
 7 import javax.persistence.Embedded;
 8 import javax.persistence.Entity;
 9 import javax.persistence.FetchType;
10 import javax.persistence.ManyToMany;
11 import javax.persistence.Version;
12 import model.BaseEntity;
13 import org.hibernate.annotations.Cascade;
14 import org.hibernate.annotations.DynamicInsert;
15 import org.hibernate.annotations.DynamicUpdate;
16 
17 @Entity
18 @DynamicInsert
19 @DynamicUpdate
20 public class Cat extends BaseEntity{
21     /**
22      * 实体类
23      */
24     private static final long serialVersionUID = -2776330321385582872L;
25     
26     private Set<Hobby> hobby;
27     private String cat_name;
28     private Name name;
29     private int version;
30 
31     @Version
32     public int getVersion() {
33         return version;
34     }
35 
36     public void setVersion(int version) {
37         this.version = version;
38     }
39 
40     public String getCat_name() {
41         return cat_name;
42     }
43 
44     public void setCat_name(String cat_name) {
45         this.cat_name = cat_name;
46     }
47 
48     @Embedded
49     @AttributeOverrides({
50             @AttributeOverride(name = "first_name", column = @Column(name = "first_name")),
51             @AttributeOverride(name = "last_name", column = @Column(name = "last_name")) })
52     public Name getName() {
53         return name;
54     }
55 
56     public void setName(Name name) {
57         this.name = name;
58     }
59     /*
60      * mappedBy属性：
61      * 如果关系是单向的，则该关联提供程序确定拥有该关系的字段。
62      * 如果关系是双向的，则将关联相反（非拥有）方上的 mappedBy 元素设置为拥
63      * 有此关系的字段或属性的名称
64      */
65     @ManyToMany( fetch = FetchType.EAGER)
66     @Cascade({org.hibernate.annotations.CascadeType.SAVE_UPDATE})
67     public Set<Hobby> getHobby() {
68         return hobby;
69     }
70 
71     public void setHobby(Set<Hobby> hobby) {
72         this.hobby = hobby;
73     }    
74 }

Hobby.java

 1 package b11_ManyToMany;
 2 import java.util.Set;
 3 import javax.persistence.Entity;
 4 import javax.persistence.FetchType;
 5 import javax.persistence.ManyToMany;
 6 import model.BaseEntity;
 7 
 8 @Entity
 9 public class Hobby extends BaseEntity {
10     /**
11      * 实体类
12      */
13     private static final long serialVersionUID = 4921844599282935594L;
14     
15     private String name;
16     private Set<Cat> cat;
17     
18     public String getName() {
19         return name;
20     }
21     public void setName(String name) {
22         this.name = name;
23     }
24     
25     @ManyToMany(fetch=FetchType.LAZY,mappedBy = "hobby")
26     public Set<Cat> getCat() {
27         return cat;
28     }
29     public void setCat(Set<Cat> cat) {
30         this.cat = cat;
31     }
32 }

组件类

 1 package b11_ManyToMany;
 2 import java.io.Serializable;
 3 import javax.persistence.Embeddable;
 4 
 5 @Embeddable
 6 public class Name implements Serializable {
 7     /**
 8      * 嵌入式组建
 9      */
10     private static final long serialVersionUID = -2776330321385582872L;
11     
12     private String first_name;
13     private String last_name;
14     public String getFirst_name() {
15         return first_name;
16     }
17     public void setFirst_name(String first_name) {
18         this.first_name = first_name;
19     }
20     public String getLast_name() {
21         return last_name;
22     }
23     public void setLast_name(String last_name) {
24         this.last_name = last_name;
25     }
26 }

Dao

 1 package daoUtil;
 2 import org.hibernate.HibernateException;
 3 import org.hibernate.Session;
 4 import org.hibernate.SessionFactory;
 5 import org.hibernate.Transaction;
 6 import org.hibernate.cfg.Configuration;
 7 import org.hibernate.service.ServiceRegistry;
 8 import org.hibernate.service.ServiceRegistryBuilder;
 9 
10 public class HibernateUtil {
11 
12     private static final SessionFactory sessionFactory;
13 
14     static {
15         try {
16             Configuration cfg = new Configuration().configure();
17             ServiceRegistry serviceRegistry = new ServiceRegistryBuilder()
18                     .applySettings(cfg.getProperties()).buildServiceRegistry();
19             sessionFactory = cfg.buildSessionFactory(serviceRegistry);
20         } catch (Throwable ex) {
21             throw new ExceptionInInitializerError(ex);
22         }
23     }
24 
25     public static Session getSession() throws HibernateException {
26         return sessionFactory.openSession();
27     }
28 
29     public static Object save(Object obj){
30         Session session = HibernateUtil.getSession();
31         Transaction tx = null;
32         try {
33             tx = session.beginTransaction();
34             session.save(obj);
35             tx.commit();
36         } catch (RuntimeException e) {
37             if (tx != null) {
38                 tx.rollback();
39             }
40             throw e;
41         } finally {
42             session.close();
43         }
44         return obj;
45     }
46     
47     public static void delete(Class<?> clazz,String id){
48         Session session = HibernateUtil.getSession();
49         Transaction tx = null;
50         try {
51             tx = session.beginTransaction();
52             Object obj = session.get(clazz,id);
53             session.delete(obj);
54             tx.commit();
55         } catch (RuntimeException e) {
56             if (tx != null) {
57                 tx.rollback();
58             }
59             throw e;
60         } finally {
61             session.close();
62         }
63     }
64 }

main

 1 package b11_ManyToMany;
 2 import java.util.HashSet;
 3 import java.util.Set;
 4 import daoUtil.HibernateUtil;
 5 
 6 public class Test_ManyToMany {
 7 
 8     private Cat save(){
 9 
10         Cat cat1 = new Cat();
11         Cat cat2 = new Cat();
12         cat1.setCat_name("b11_ManyToMany1");
13         cat1.setName(new Name());
14         
15         cat2.setCat_name("b11_ManyToMany2");
16         cat2.setName(new Name());
17         
18         Set<Hobby> hobbies = new HashSet<Hobby>();
19         
20         Hobby hobby1 = new Hobby();
21         hobby1.setName("足球");
22         hobbies.add(hobby1);
23         
24         Hobby hobby2 = new Hobby();
25         hobby2.setName("篮球");
26         hobbies.add(hobby2);
27         
28         cat1.setHobby(hobbies);
29         cat2.setHobby(hobbies);
30         
31         HibernateUtil.save(cat1);
32         HibernateUtil.save(cat2);
33         System.out.println(cat1.getId());
34         System.out.println(cat2.getId());
35         return cat1;
36     }
37     
38     public static void main(String[] args) {
39         // 通过cat加载hobby
40         Cat cat = new Test_ManyToMany().save();
41         
42         Cat cat1 = (Cat)HibernateUtil.getSession().get(Cat.class, cat.getId());
43         System.out.println(cat1.getId());
44         
45         Set<Hobby> hobbies = cat1.getHobby();
46         for (Hobby hobby : hobbies) {
47             System.out.println(hobby.getName());
48         }
49         // delete
50 //        HibernateUtil.delete(Cat.class,"402880854c75601d014c75602f9f0000");
51         
52         // 通过hobby加载cat
53 //        Hobby hobby = (Hobby)HibernateUtil.getSession().get(Hobby.class, "402880854c75601d014c75602fbb0001");
54 //        System.out.println(hobby.getId());
55 //        
56 //        Set<Cat> cats = hobby.getCat();
57 //        for (Cat cat2 : cats) {
58 //            System.out.println(cat2.getCat_name());
59 //        }
60     }
61 }

环境：JDK1.6，MAVEN，tomcat，eclipse

源码地址：http://files.cnblogs.com/files/xiluhua/hibernate%40ManyToMany.rar

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原文地址：https://www.cnblogs.com/xiluhua/p/4385615.html