一、Hibernate处理关系
关系主要有三种：1、多对一 2、一对多 3、多对多
1、多对一
一个Product对应一个Category，一个Category对应多个Product（一个产品对应一个类别，一个类别对应多个产品）
也就是Product和Category是多对一的关系。（多个产品对应一个类别）
1.1在数据test下创建表category_table,两个字段，id（自增），字符串格式name
其实也不用建表，因为Hibernate会自动建表。
use test; CREATE TABLE category_ table( id int(11) NOT NULL AUTO_INCREMENT, name varchar(30) , PRIMARY KEY (id)) DEFAULT CHARSET=UTF8;
1.2、准备类别实体类（Category.java）
package com.demo.pojopublic class Category{ ???private int id;//类别id ???private String name;//类别名称 ???????//属性的getter/setter方法 ???public int getId(){ ???????return id; ???} ???public void setId(int id){ ???????this.id=id; ???} ???public String getName(){ ???????return name; ???} ???public void setName(String name){ ???????this.name=name; ???}}1.3、准备类别实体类的映射xml（Category.hbm.xml）
<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC ???????"-//Hibernate/Hibernate Mapping DTD 3.0//EN" ???????"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.how2java.pojo"> ???<class name="Category" table="category_table"> ???????<id name="id" column="id"> ???????????<generator class="native"> ???????????</generator> ???????</id> ???????<property name="name" /> ???</class> ???</hibernate-mapping>
1.4、为产品实体类（Product.java）增加Category属性
package com.how2java.pojo;public class Product { ???int id; ???String name; ???float price; ???????//增加Category的属性 ???Category category; ???public Category getCategory() { ???????return category; ???} ???public void setCategory(Category category) { ???????this.category = category; ???} ???public int getId() { ???????return id; ???} ???public void setId(int id) { ???????this.id = id; ???} ???public String getName() { ???????return name; ???} ???public void setName(String name) { ???????this.name = name; ???} ???public float getPrice() { ???????return price; ???} ???public void setPrice(float price) { ???????this.price = price; ???} ???}1.5、为产品映射xml文件（Product.hbm.xml）设置Category多对一关系
<many-to-one name="category" class="Category" column="cid" />
使用many-to-one标签设置多对一关系，name="category"，对应Product类中的category属性
class="Category"表示对应Category类，column="cid"表示指向category_table的外键。
具体配置xml如下：
<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC ???????"-//Hibernate/Hibernate Mapping DTD 3.0//EN" ???????"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.how2java.pojo"> ???<class name="Product" table="product_"> ???????<id name="id" column="id"> ???????????<generator class="native"> ???????????</generator> ???????</id> ???????<property name="name" /> ???????<property name="price" /> ???????<many-to-one name="category" class="Category" column="cid" /> ???</class> ???</hibernate-mapping>
1.6、在hibernate.cfg.xml中增加Category的映射文件
<?xml version=‘1.0‘ encoding=‘utf-8‘?><!DOCTYPE hibernate-configuration PUBLIC ??????"-//Hibernate/Hibernate Configuration DTD 3.0//EN""http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"><hibernate-configuration> ???<session-factory> ???????<!-- Database connection settings --> ???????<property name="connection.driver_class">com.mysql.jdbc.Driver</property> ???????<property name="connection.url">jdbc:mysql://localhost:3306/test?characterEncoding=GBK</property> ???????<property name="connection.username">root</property> ???????<property name="connection.password">admin</property> ???????<!-- SQL dialect --> ???????<property name="dialect">org.hibernate.dialect.MySQLDialect</property> ???????<property name="current_session_context_class">thread</property> ???????<property name="show_sql">true</property> ???????<property name="hbm2ddl.auto">update</property> ???????<!--Product实体类的映射文件--> ???????<mapping resource="com/demo/pojo/Product.hbm.xml" /> ???????<!--Category实体类的映射文件--> ???????<mapping resource="com/demo/pojo/Category.hbm.xml" /> ???</session-factory></hibernate-configuration>
1.7测试many-to-one多对一关系
package com.demo.test;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;import com.demo.pojo.Product;public class TestHibernate{ ???public static void main(String[] args){ ???????SessionFactory sf=new Configuration().configure().buildSessionFactory(); ???????Session session=sf.opneSession(); ???????session.beginTransaction(); ???????????????Category category=new Category(); ???????category.setName("car"); ???????session.save(category); ???????????????Product product=(Product)s.get(Product.clas,5);//获取id=5的产品 ???????product.setCategory(category);//把类别设置到产品的实体类中 ???????session.update(p); ???????????????session.getTransaction().commint(); ???????session.close(); ???????sf.close(); ???}}2、一对多
Category和Product是一对多关系（一个Category对应多个Product）
2.1、给Category实体类增加一个Set集合（无序的Product）
package com.demo.pojoimport java.util.Set;public class Category{ ???private int id;//类别id ???private String name;//类别名称 ???????//属性的getter/setter方法 ???public int getId(){ ???????return id; ???} ???public void setId(int id){ ???????this.id=id; ???} ???public String getName(){ ???????return name; ???} ???public void setName(String name){ ???????this.name=name; ???} ???????//设置Product的Set ???Set<Product> products; ???public Set<Product> getProducts(){ ???????return products; ???} ???public void SetProducts(Set<Product> products){ ???????this.products=products; ???}}2.2、给Category.hbm.xml增加one-to-many映射
<set name="products" lazy="false"> ???<key column="cid" not-null="false"/> ???<ont-to-many class="Product"/></set>
set标签用于设置一对多关系，也可以设置多对多。
name="products"对应Category类中的products属性，lazy="false"，表示不使用延迟加载
<key colum="cid" not-null="false"/>表示外键是cid，可以为空
<one-to-many class="Product"/>表示一对多对应的类是Product
<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC ???????"-//Hibernate/Hibernate Mapping DTD 3.0//EN" ???????"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.how2java.pojo"> ???<class name="Category" table="category_"> ???????<id name="id" column="id"> ???????????<generator class="native"> ???????????</generator> ???????</id> ???????<property name="name" /> ???????<!--set标签设置一对多关系--> ???????<set name="products" lazy="false"> ???????????<key column="cid" not-null="false" /> ???????????<one-to-many class="Product" /> ???????</set> ???????????????????</class> ???</hibernate-mapping>
2.3、测试one-to-many关系
首先获取id=i的category，然后通过getProducts()获取所对应的所有的product
package com.demo.test;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;import com.demo.pojo.Product;public class TestHibernate{ ???public static void main(String[] args){ ???????SessionFactory sf=new Configuration().configure().buildSessionFactory(); ???????Session session=sf.opneSession(); ???????session.beginTransaction(); ???????????????Category category=new Category(); ???????category.setName("car"); ???????session.save(category); ???????????????Category category=(Category)session.get(Category.class,1);//获取id=1的类别 ???????Set<Product> set=c.getProducts();//获取产品的集合 ???????for(Product p:set){//遍历产品集合 ???????????System.out.println(p.getName()); ???????} ???????session.getTransaction().commint(); ???????session.close(); ???????sf.close(); ???}}3、多对多
一种product可以被多个User购买，一个User可以购买多种Product
所以Product和User之间关系是多对多many-to-many
要实现多对多关系，必须要有一张中间表，user_product用于维护User和Product之间的关系
3.1、User的实体类（User.java）
增加Product集合
package com.demo.pojo;import java.util.Set;public class User{ ???private int id;//用户id ???private String name;//用户名 ???Set<Product> products;//产品 ???????//属性的getter/setter方法 ???public int getId(){ ???????return id; ???} ???public void setId(int id){ ???????this.id=id; ???} ???public int getName(){ ???????return name; ???} ???public void setName(String name){ ???????this.name=name; ???} ???//设置Product的Set ???public Set<Product> getProducts(){ ???????return products; ???} ???public void setProducts(Set<Product> products){ ???????this.products=products; ???}}3.2、User.hbm.xml映射文件xml的编写
<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC ???????"-//Hibernate/Hibernate Mapping DTD 3.0//EN" ???????"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.how2java.pojo"> ???<class name="User" table="user_"> ???????<id name="id" column="id"> ???????????<generator class="native"> ???????????</generator> ???????</id> ???????<property name="name" /> ???????????????<!--配置Product与User的多对多关系，中间表是user_product--> ???????<set name="products" table="user_product" lazy="false"> ???????????<key column="uid" /> ???????????<many-to-many column="pid" class="Product" /> ???????</set> ???????????????????</class> ???</hibernate-mapping>
3.3、Product的实体类（Product.java）
增加User的集合
package com.demo.pojo;import java.util.Set;public class Product{ ???private int id; ???private String name; ???private float price; ???????Category category;//一对多 ???????Set<User> users;//多对多 ???????//属性的getter/setter方法 ???public int getId(){ ???????return id; ???} ???public void setId(int id){ ???????this.id=id; ???} ???public String getName(){ ???????return name; ???} ???public void setName(String name){ ???????this.name=name; ???} ???public float getPrice(){ ???????return price; ???} ???public void setPrice(float price){ ???????this.price=price; ???} ???????//Category ???public Category getCategory(){ ???????return category; ???} ???public void setCategory(Category category){ ???????this.category=category; ???} ???//Set<User> ???public Set<User> getUser(){ ???????return users; ???} ???public vodi setUser(Set<User> users){ ???????this.users=users; ???}}3.4、Product的映射文件配置（Product.hbm.xml）
<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC ???????"-//Hibernate/Hibernate Mapping DTD 3.0//EN" ???????"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.how2java.pojo"> ???<class name="Product" table="product_"> ???????<id name="id" column="id"> ???????????<generator class="native"> ???????????</generator> ???????</id> ???????<property name="name" /> ???????<property name="price" /> ???????????????<!--多对一--> ???????<many-to-one name="category" class="Category" column="cid" /> ???????<!-- 多对多--> ???????<set name="users" table="user_product" lazy="false"> ???????????<key column="pid" /> ???????????<many-to-many column="uid" class="User" /> ???????</set> ???????????????????????????</class> ???</hibernate-mapping>
3.5、在hibernate.cfg.xml中增加User.hbm.xml的映射
<?xml version=‘1.0‘ encoding=‘utf-8‘?><!DOCTYPE hibernate-configuration PUBLIC ??????"-//Hibernate/Hibernate Configuration DTD 3.0//EN""http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"><hibernate-configuration> ???<session-factory> ???????<!-- Database connection settings --> ???????<property name="connection.driver_class">com.mysql.jdbc.Driver</property> ???????<property name="connection.url">jdbc:mysql://localhost:3306/test?characterEncoding=GBK</property> ???????<property name="connection.username">root</property> ???????<property name="connection.password">admin</property> ???????<!-- SQL dialect --> ???????<property name="dialect">org.hibernate.dialect.MySQLDialect</property> ???????<property name="current_session_context_class">thread</property> ???????<property name="show_sql">true</property> ???????<property name="hbm2ddl.auto">update</property> ???????<!--映射文件的配置--> ???????<mapping resource="com/demo/pojo/Product.hbm.xml" /> ???????<mapping resource="com/demo/pojo/Category.hbm.xml" /> ???????<mapping resource="com/demo/pojo/User.hbm.xml" /> ???</session-factory></hibernate-configuration>
3.6、测试多对多many-to-many关系
package com.demo.test;import java.util.HashSet;import java.util.Set;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;import com.demo.pojo.Product;import com.demo.pojo.User;public class TestHibernate{ ???public static void main(String[] args){ ???????SessionFactory sf=new Configuration().configure().buildSessionFactory(); ???????Session session=sf.opneSession(); ???????session.beginTransaction(); ???????//增加3个用户 ???????Set<User> users=new HashSet(); ???????for(int i=0;i<3;i++){ ???????????User u=new User(); ???????????u.setName("user"+i); ???????????users.add(u); ???????????s.save(u); ???????} ???????//id=1产品被用户1,2,3购买 ???????Product product=(Product)session.get(Product.class,1); ???????product.setUsers(users); ???????s.save(product); ???????????????session.getTransaction().commint(); ???????session.close(); ???????sf.close(); ???}}三、持久层框架（Hibernate）
原文地址：https://www.cnblogs.com/drq1/p/8514736.html