- 背景：
在实际开发中我们会遇到表的多对多关联，比如：一篇博客文章，它可以同时属于JAVA分类、Hibernate分类。
因此，我们在hibernate的学习文章系列中，需要学会如何使用hibernate来实现多对多的关联关系。
在hibernate实现多对多的关联关系中，也是需要创建一个中间表来存储、维护两张表的多对多的关系。具体实现有两种可选方案：单向多对多、双向多对多。
- 单向多对多：
新建一个java project，定义项目名称为：hibernate07；在src下添加hibernate.cfg.xml
1 <?xml version="1.0" encoding="UTF-8"?> 2 <!DOCTYPE hibernate-configuration PUBLIC 3 "-//Hibernate/Hibernate Configuration DTD 3.0//EN" 4 "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"> 5 <hibernate-configuration> 6 <session-factory> 7 <property name="hibernate.connection.username">root</property> 8 <property name="hibernate.connection.password">123456</property> 9 <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property> 10 <property name="hibernate.connection.url">jdbc:mysql://localhost/hibernate_01</property> 11 12 <!-- <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property> 13 <property name="hibernate.dialect">org.hibernate.dialect.MySQLInnoDBDialect</property> --> 14 <property name="hibernate.dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property> 15 16 <property name="hibernate.show_sql">true</property> 17 18 <property name="hibernate.format_sql">true</property> 19 20 <property name="hibernate.hbm2ddl.auto">update</property> 21 22 <property name="hibernate.current_session_context_class">thread</property> 23 24 <property name="hibernate.c3p0.max_size">500</property> 25 <property name="hibernate.c3p0.min_size">20</property> 26 <property name="hibernate.c3p0.max_statements">10</property> 27 <property name="hibernate.c3p0.timeout">2000</property> 28 <property name="hibernate.c3p0.idle_test_period">2000</property> 29 <property name="hibernate.c3p0.acquire_increment">10</property> 30 31 <mapping resource="com/dx/hibernate06/n2n/ProductCategory.hbm.xml" /> 32 <mapping resource="com/dx/hibernate06/n2n/ProductItem.hbm.xml" /> 33 34 </session-factory> 35 </hibernate-configuration>
在src下创建包com.dx.hibernate06.n2n,在包下创建：
ProductCategory.java(在category这个类中创建了一个Set<ProductItem> productItems 属性)
1 package com.dx.hibernate06.n2n;
2
3 import java.util.HashSet;
4 import java.util.Set;
5
6 public class ProductCategory {
7 private Integer id;
8 private String name;
9 private String detail;
10 private Set<ProductItem> productItems = new HashSet<>();
11
12 public ProductCategory() {
13
14 }
15
16 public ProductCategory(String name, String detail) {
17 super();
18 this.name = name;
19 this.detail = detail;
20 }
21
22 public Integer getId() {
23 return id;
24 }
25
26 public void setId(Integer id) {
27 this.id = id;
28 }
29
30 public String getName() {
31 return name;
32 }
33
34 public void setName(String name) {
35 this.name = name;
36 }
37
38 public String getDetail() {
39 return detail;
40 }
41
42 public void setDetail(String detail) {
43 this.detail = detail;
44 }
45
46 public Set<ProductItem> getProductItems() {
47 return productItems;
48 }
49
50 public void setProductItems(Set<ProductItem> productItems) {
51 this.productItems = productItems;
52 }
53
54 }
ProductCategory.hbm.xml
1 <?xml version="1.0"?> 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> 4 <!-- Generated 2017-6-7 22:33:53 by Hibernate Tools 3.5.0.Final --> 5 <hibernate-mapping package="com.dx.hibernate06.n2n"> 6 <class name="ProductCategory" table="PRODUCT_CATEGORY"> 7 <id name="id" type="java.lang.Integer"> 8 <column name="ID" /> 9 <generator class="native" /> 10 </id> 11 <property name="name" type="java.lang.String"> 12 <column name="NAME" /> 13 </property> 14 <property name="detail" type="java.lang.String"> 15 <column name="DETAIL" /> 16 </property> 17 18 <set name="productItems" table="PRODUCT_CATEGORY_ITEM"> 19 <key> 20 <column name="CATEGORY_ID" /> 21 </key> 22 <many-to-many class="ProductItem" column="ITEM_ID"></many-to-many> 23 </set> 24 </class> 25 </hibernate-mapping>
备注：在ProductCategory.hbm.xml的set节点我们定义的table属性，并定义了many-to-many节点用来指向ProductItem。
ProductItem.java
1 package com.dx.hibernate06.n2n;
2
3 public class ProductItem {
4 private Integer id;
5 private String title;
6 private double price;
7
8 public ProductItem() {
9 }
10
11 public ProductItem(String title, double price) {
12 super();
13 this.title = title;
14 this.price = price;
15 }
16
17 public Integer getId() {
18 return id;
19 }
20
21 public void setId(Integer id) {
22 this.id = id;
23 }
24
25 public String getTitle() {
26 return title;
27 }
28
29 public void setTitle(String title) {
30 this.title = title;
31 }
32
33 public double getPrice() {
34 return price;
35 }
36
37 public void setPrice(double price) {
38 this.price = price;
39 }
40
41 }
ProductItem.hbm.xml
1 <?xml version="1.0"?> 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> 4 <!-- Generated 2017-6-7 22:33:53 by Hibernate Tools 3.5.0.Final --> 5 <hibernate-mapping> 6 <class name="com.dx.hibernate06.n2n.ProductItem" table="PRODUCT_ITEM"> 7 <id name="id" type="java.lang.Integer"> 8 <column name="ID" /> 9 <generator class="native" /> 10 </id> 11 <property name="title" type="java.lang.String"> 12 <column name="TITLE" /> 13 </property> 14 <property name="price" type="double"> 15 <column name="PRICE" /> 16 </property> 17 </class> 18 </hibernate-mapping>
测试类TestMain.java
1 package com.dx.hibernate06.n2n;
2
3 import java.util.Date;
4 import java.util.Set;
5
6 import org.hibernate.Session;
7 import org.hibernate.SessionFactory;
8 import org.hibernate.Transaction;
9 import org.hibernate.boot.Metadata;
10 import org.hibernate.boot.MetadataSources;
11 import org.hibernate.boot.model.naming.ImplicitNamingStrategyComponentPathImpl;
12 import org.hibernate.boot.registry.StandardServiceRegistry;
13 import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
14 import org.hibernate.metamodel.internal.MapMember;
15 import org.junit.After;
16 import org.junit.Before;
17 import org.junit.Test;
18
19 public class TestMain {
20 private SessionFactory sessionFactory = null;
21 private Session session = null;
22 private Transaction transaction = null;
23
24 @Before
25 public void init() {
26 StandardServiceRegistry standardRegistry = new StandardServiceRegistryBuilder().configure().build();
27 Metadata metadata = new MetadataSources(standardRegistry).getMetadataBuilder().applyImplicitNamingStrategy(ImplicitNamingStrategyComponentPathImpl.INSTANCE).build();
28
29 sessionFactory = metadata.getSessionFactoryBuilder().build();
30 session = sessionFactory.getCurrentSession();
31 transaction = session.beginTransaction();
32 }
33
34 @After
35 public void destory() {
36 transaction.commit();
37 session.close();
38 sessionFactory.close();
39 }
40 }
测试代码：
添加测试函数1：
1 @Test
2 public void testInsert() {
3 ProductCategory category1 = new ProductCategory();
4 category1.setName("category1");
5 category1.setDetail("Detail");
6
7 ProductCategory category2 = new ProductCategory();
8 category2.setName("category2");
9 category2.setDetail("Detail");
10
11 ProductItem item1 = new ProductItem();
12 item1.setTitle("item1");
13 item1.setPrice(110.00);
14
15 ProductItem item2 = new ProductItem();
16 item2.setTitle("item2");
17 item2.setPrice(110.00);
18
19 category1.getProductItems().add(item1);
20 category1.getProductItems().add(item2);
21
22 category2.getProductItems().add(item1);
23 category2.getProductItems().add(item2);
24
25 session.save(category1);
26 session.save(category2);
27
28 session.save(item1);
29 session.save(item2);
30 }
控制台打印sql
1 Hibernate: 2 3 create table PRODUCT_CATEGORY ( 4 ID integer not null auto_increment, 5 NAME varchar(255), 6 DETAIL varchar(255), 7 primary key (ID) 8 ) engine=InnoDB 9 Hibernate: 10 11 create table PRODUCT_CATEGORY_ITEM ( 12 CATEGORY_ID integer not null, 13 ITEM_ID integer not null, 14 primary key (CATEGORY_ID, ITEM_ID) 15 ) engine=InnoDB 16 Hibernate: 17 18 create table PRODUCT_ITEM ( 19 ID integer not null auto_increment, 20 TITLE varchar(255), 21 PRICE double precision, 22 primary key (ID) 23 ) engine=InnoDB 24 Hibernate: 25 26 alter table PRODUCT_CATEGORY_ITEM 27 add constraint FKgqq9f2yg5b52m390yk15c8u28 28 foreign key (ITEM_ID) 29 references PRODUCT_ITEM (ID) 30 Hibernate: 31 32 alter table PRODUCT_CATEGORY_ITEM 33 add constraint FKtajc52s55t4fk8864s63hsuv2 34 foreign key (CATEGORY_ID) 35 references PRODUCT_CATEGORY (ID)
查询数据库结果信息：
添加测试函数2：
1 @Test
2 public void testSelect() {
3 ProductCategory category = (ProductCategory) session.get(ProductCategory.class, 1);
4 System.out.println(category.getName());
5
6 System.out.println(category.getProductItems().size());
7 }
后台执行sql及结果:
1 Hibernate: 2 select 3 productcat0_.ID as ID1_0_0_, 4 productcat0_.NAME as NAME2_0_0_, 5 productcat0_.DETAIL as DETAIL3_0_0_ 6 from 7 PRODUCT_CATEGORY productcat0_ 8 where 9 productcat0_.ID=? 10 category1 11 Hibernate: 12 select 13 productite0_.CATEGORY_ID as CATEGORY1_1_0_, 14 productite0_.ITEM_ID as ITEM_ID2_1_0_, 15 productite1_.ID as ID1_2_1_, 16 productite1_.TITLE as TITLE2_2_1_, 17 productite1_.PRICE as PRICE3_2_1_ 18 from 19 PRODUCT_CATEGORY_ITEM productite0_ 20 inner join 21 PRODUCT_ITEM productite1_ 22 on productite0_.ITEM_ID=productite1_.ID 23 where 24 productite0_.CATEGORY_ID=? 25 2
- 双向多对多：
实现双向多对多，需要再ProductItem的另一端也定义Set属性：Set<ProductCategory> productCategories。还需要在ProductItem.hbm.xml中添加set节点，节点属性配置与ProductCategory.hbm.xml中set节点配置对调。
修改ProductItem.java（在类中添加属性：Set<ProductCategory> productCategories）:
1 package com.dx.hibernate06.n2n;
2
3 import java.util.HashSet;
4 import java.util.Set;
5
6 public class ProductItem {
7 private Integer id;
8 private String title;
9 private double price;
10 private Set<ProductCategory> productCategories = new HashSet<>();
11
12 public ProductItem() {
13 }
14
15 public ProductItem(String title, double price) {
16 super();
17 this.title = title;
18 this.price = price;
19 }
20
21 public Integer getId() {
22 return id;
23 }
24
25 public void setId(Integer id) {
26 this.id = id;
27 }
28
29 public String getTitle() {
30 return title;
31 }
32
33 public void setTitle(String title) {
34 this.title = title;
35 }
36
37 public double getPrice() {
38 return price;
39 }
40
41 public void setPrice(double price) {
42 this.price = price;
43 }
44
45 public Set<ProductCategory> getProductCategories() {
46 return productCategories;
47 }
48
49 public void setProductCategories(Set<ProductCategory> productCategories) {
50 this.productCategories = productCategories;
51 }
52
53 }
修改ProductItem.hbm.xml配置文件（添加set节点，并在ProductItem.hbm.xml或者ProductCategory.hbm.xml的set节点中添加属性inverse="true"）：
1 <?xml version="1.0"?> 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> 4 <!-- Generated 2017-6-7 22:33:53 by Hibernate Tools 3.5.0.Final --> 5 <hibernate-mapping> 6 <class name="com.dx.hibernate06.n2n.ProductItem" table="PRODUCT_ITEM"> 7 <id name="id" type="java.lang.Integer"> 8 <column name="ID" /> 9 <generator class="native" /> 10 </id> 11 <property name="title" type="java.lang.String"> 12 <column name="TITLE" /> 13 </property> 14 <property name="price" type="double"> 15 <column name="PRICE" /> 16 </property> 17 18 <set name="productCategories" table="PRODUCT_CATEGORY_ITEM" inverse="true"> 19 <key> 20 <column name="ITEM_ID" /> 21 </key> 22 <many-to-many class="com.dx.hibernate06.n2n.ProductCategory" column="CATEGORY_ID"></many-to-many> 23 </set> 24 </class> 25 </hibernate-mapping>
删除数据中的表，之后添加测试函数。
mysql> drop table PRODUCT_CATEGORY_ITEM; Query OK, 0 rows affected (0.02 sec) mysql> drop table PRODUCT_CATEGORY; Query OK, 0 rows affected (0.02 sec) mysql> drop table PRODUCT_ITEM; Query OK, 0 rows affected (0.01 sec) mysql> show tables; +------------------------+ | Tables_in_hibernate_01 | +------------------------+ | customer | | deparments | | managers | | member | | memberdetail | | news | | orders | +------------------------+ 7 rows in set (0.00 sec) mysql>
测试代码：
添加测试函数1：
1 @Test
2 public void testInsert() {
3 ProductCategory category1 = new ProductCategory();
4 category1.setName("category1");
5 category1.setDetail("Detail");
6
7 ProductCategory category2 = new ProductCategory();
8 category2.setName("category2");
9 category2.setDetail("Detail");
10
11 ProductItem item1 = new ProductItem();
12 item1.setTitle("item1");
13 item1.setPrice(110.00);
14
15 ProductItem item2 = new ProductItem();
16 item2.setTitle("item2");
17 item2.setPrice(110.00);
18
19 category1.getProductItems().add(item1);
20 category1.getProductItems().add(item2);
21 category2.getProductItems().add(item1);
22 category2.getProductItems().add(item2);
23
24 item1.getProductCategories().add(category1);
25 item1.getProductCategories().add(category2);
26 item2.getProductCategories().add(category1);
27 item2.getProductCategories().add(category2);
28
29 session.save(category1);
30 session.save(category2);
31
32 session.save(item1);
33 session.save(item2);
34 }
测试执行sql:
1 Hibernate: 2 3 create table PRODUCT_CATEGORY ( 4 ID integer not null auto_increment, 5 NAME varchar(255), 6 DETAIL varchar(255), 7 primary key (ID) 8 ) engine=InnoDB 9 Hibernate: 10 11 create table PRODUCT_CATEGORY_ITEM ( 12 CATEGORY_ID integer not null, 13 ITEM_ID integer not null, 14 primary key (CATEGORY_ID, ITEM_ID) 15 ) engine=InnoDB 16 Hibernate: 17 18 create table PRODUCT_ITEM ( 19 ID integer not null auto_increment, 20 TITLE varchar(255), 21 PRICE double precision, 22 primary key (ID) 23 ) engine=InnoDB 24 Hibernate: 25 26 alter table PRODUCT_CATEGORY_ITEM 27 add constraint FKgqq9f2yg5b52m390yk15c8u28 28 foreign key (ITEM_ID) 29 references PRODUCT_ITEM (ID) 30 Hibernate: 31 32 alter table PRODUCT_CATEGORY_ITEM 33 add constraint FKtajc52s55t4fk8864s63hsuv2 34 foreign key (CATEGORY_ID) 35 references PRODUCT_CATEGORY (ID) 36 Hibernate: 37 insert 38 into 39 PRODUCT_CATEGORY 40 (NAME, DETAIL) 41 values 42 (?, ?) 43 Hibernate: 44 insert 45 into 46 PRODUCT_CATEGORY 47 (NAME, DETAIL) 48 values 49 (?, ?) 50 Hibernate: 51 insert 52 into 53 PRODUCT_ITEM 54 (TITLE, PRICE) 55 values 56 (?, ?) 57 Hibernate: 58 insert 59 into 60 PRODUCT_ITEM 61 (TITLE, PRICE) 62 values 63 (?, ?) 64 Hibernate: 65 insert 66 into 67 PRODUCT_CATEGORY_ITEM 68 (CATEGORY_ID, ITEM_ID) 69 values 70 (?, ?) 71 Hibernate: 72 insert 73 into 74 PRODUCT_CATEGORY_ITEM 75 (CATEGORY_ID, ITEM_ID) 76 values 77 (?, ?) 78 Hibernate: 79 insert 80 into 81 PRODUCT_CATEGORY_ITEM 82 (CATEGORY_ID, ITEM_ID) 83 values 84 (?, ?) 85 Hibernate: 86 insert 87 into 88 PRODUCT_CATEGORY_ITEM 89 (CATEGORY_ID, ITEM_ID) 90 values 91 (?, ?)
在数据中执行查询：
时间： 2024-11-10 11:34:12