《Hibernate上课笔记》------class6------Hibernate实现一对多关联映射

一：一对多关联概念

1.实体一对多关联（1：n）

定义：

如果对于实体集A中的每一个实体，实体集B中有n个实体（n>=0）与之联系，反之，对于实体集B中的每一个实体，实体集A中至多只有一个实体与之联系，则称实体集A与实体集B有一对多联系，记为1：n。
实例：一个班级中有若干名学生，每个学生只在一个班级中学习。

示例：在一些购物网站中，用户和订单之间的关系就是一对多关联关系（一个用户可以有多个订单，而一个订单只属于一个用户。）

2.数据库一对多关联

在关系模型中，只存在外键参照关系，而且是many方参照one方。

二：Hibernate实现单向一对多关联

引例：
通常情况下，在一些购物网站系统中，用户和订单之间的关系就是一对多关联关系，并且对于用户来说需要知道自己有哪些订单，对于商家来说需要知道某个订单属于哪个用户，思考这种情况该如何实现？

1.xml配置实现

用户类：

public class User {private int id;private String userName;private String passWord;private Set<Order> orders = new HashSet<>();public int getId() {return id;}public void setId(int id) {this.id = id;}public String getUserName() {return userName;}public void setUserName(String userName) {this.userName = userName;}public String getPassWord() {return passWord;}public void setPassWord(String passWord) {this.passWord = passWord;}public Set<Order> getOrders() {return orders;}public void setOrders(Set<Order> orders) {this.orders = orders;}@Overridepublic String toString() {return "User [id=" + id + ", userName=" + userName + ", passWord=" + passWord + ", orders=" + orders + "]";}}

用户配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.hibernate.entity"><class name="User" table="user"><id name="id" type="int"><column name="id"></column><generator class="native"></generator></id><property name="userName" column="user_name"type="java.lang.String"></property><property name="passWord" column="password"type="java.lang.String" /><set name="orders" cascade="all"><key column="user_id"></key><one-to-many class="Order" /></set></class>
</hibernate-mapping>

订单类：

public class Order {private int id;private int price;public int getId() {return id;}public void setId(int id) {this.id = id;}@Overridepublic String toString() {return "Order [id=" + id + ", price=" + price + ", getId()=" + getId() + ", getClass()=" + getClass()+ ", hashCode()=" + hashCode() + ", toString()=" + super.toString() + "]";}public int getPrice() {return price;}public void setPrice(int price) {this.price = price;}}

订单配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.hibernate.entity"><class name="Order" table="n_order"><id name="id" type="int"><column name="id"></column><generator class="increment"></generator></id><property name="price"></property></class>
</hibernate-mapping>

测试类：

public class Test {public static void main(String[] args) {// 保存用户// saveUser();// 保存订单// saveOrders();// 根据用户查找订单// findOrderByUserId();// 根据用户id删除订单deleteOrderByUserId();}public static void saveUser() {// 1.获取session对象Session session = HibernateUtil.openSession();Transaction tx = session.beginTransaction();User user = new User();user.setUserName("张三");user.setPassWord("123");session.save(user);tx.commit();session.close();// 5.关闭sessionFactory}public static void saveOrders() {// 1.获取session对象Session session = HibernateUtil.openSession();Transaction tx = session.beginTransaction();User user = session.get(User.class, new Integer(1));Set<Order> orders = user.getOrders();for (int i = 0; i < 3; i++) {Order order = new Order();order.setPrice(35);orders.add(order);}user.setOrders(orders);session.save(user);tx.commit();session.close();// 5.关闭sessionFactory}public static void findOrderByUserId() {Session session = HibernateUtil.openSession();Transaction tx = session.beginTransaction();User user = session.get(User.class, new Integer(1));System.out.println(user.toString());tx.commit();session.close();// 5.关闭sessionFactory}public static void deleteOrderByUserId() {Session session = HibernateUtil.openSession();Transaction tx = session.beginTransaction();User user = session.get(User.class, new Integer(1));session.delete(user);tx.commit();session.close();// 5.关闭sessionFactory}
}

当使用list集合映射时，需要在order表中添加一个额外字段来表示插入顺序

配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.hibernate.entity"><class name="User" table="user"><id name="id" type="int"><column name="id"></column><generator class="native"></generator></id><property name="userName" column="user_name"type="java.lang.String"></property><property name="passWord" column="password"type="java.lang.String" /><list name="orders" cascade="all"><key column="user_id"></key><index column="order_index"></index><one-to-many class="Order" /></list></class>
</hibernate-mapping>

当使用Map集合映射时，需要在Order表中添加也给额外字段来记录Map中key的值

映射配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.hibernate.entity"><class name="User" table="user"><id name="id" type="int"><column name="id"></column><generator class="native"></generator></id><property name="userName" column="user_name"type="java.lang.String"></property><property name="passWord" column="password"type="java.lang.String" /><map name="orders" cascade="all"><key column="user_id"></key><index column="order_key" type="string"></index><one-to-many class="Order" /></map></class>
</hibernate-mapping>

二：Hibernate双向一对多关联

目的：通过用户可以找到订单，通过订单也可以找到用户

1.使用xml文件方式完成配置

数据库表结构同上，只是配置文件发生改变
User类：

public class User {private int id;private String userName;private String passWord;private Map<String, Order> orders = new HashMap<>();public int getId() {return id;}public void setId(int id) {this.id = id;}public String getUserName() {return userName;}public void setUserName(String userName) {this.userName = userName;}public String getPassWord() {return passWord;}public void setPassWord(String passWord) {this.passWord = passWord;}public Map<String, Order> getOrders() {return orders;}public void setOrders(Map<String, Order> orders) {this.orders = orders;}@Overridepublic String toString() {return "User [id=" + id + ", userName=" + userName + ", passWord=" + passWord + ", orders=" + orders + "]";}}

User类配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.hibernate.entity"><class name="User" table="user"><id name="id" type="int"><column name="id"></column><generator class="native"></generator></id><property name="userName" column="user_name"type="java.lang.String"></property><property name="passWord" column="password"type="java.lang.String" /><map name="orders" cascade="all"><key column="user_id"></key><index column="order_key" type="string"></index><one-to-many class="Order" /></map></class>
</hibernate-mapping>

Order类：

public class Order {private int id;private int price;private User user;public User getUser() {return user;}public void setUser(User user) {this.user = user;}public int getId() {return id;}public void setId(int id) {this.id = id;}@Overridepublic String toString() {return "Order [id=" + id + ", price=" + price + ", getId()=" + getId() + ", getClass()=" + getClass()+ ", hashCode()=" + hashCode() + ", toString()=" + super.toString() + "]";}public int getPrice() {return price;}public void setPrice(int price) {this.price = price;}}

Order类配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.hibernate.entity"><class name="Order" table="n_order2"><id name="id" type="int"><column name="id"></column><generator class="increment"></generator></id><property name="price"></property><many-to-one name="user" column="user_id" class="User"></many-to-one></class>
</hibernate-mapping>

2.使用注解方式完成配置

User类：


@Entity
@Table(name = "user")
public class User {private int id;private String userName;private String passWord;private Map<String, Order> orders = new HashMap<>();@Id@GeneratedValue(generator = "nat")@GenericGenerator(name = "nat", strategy = "native")public int getId() {return id;}public void setId(int id) {this.id = id;}@Column(name = "user_name")public String getUserName() {return userName;}public void setUserName(String userName) {this.userName = userName;}public String getPassWord() {return passWord;}public void setPassWord(String passWord) {this.passWord = passWord;}@OneToMany(mappedBy = "user", targetEntity = Order.class, cascade = CascadeType.ALL)@MapKeyColumn(name = "order_key")public Map<String, Order> getOrders() {return orders;}public void setOrders(Map<String, Order> orders) {this.orders = orders;}@Overridepublic String toString() {return "User [id=" + id + ", userName=" + userName + ", passWord=" + passWord + ", orders=" + orders + "]";}}

Order类：

@Entity
@Table(name = "n_order2")
public class Order {private int id;private int price;private User user;@ManyToOne@JoinColumn(name = "user_id")public User getUser() {return user;}public void setUser(User user) {this.user = user;}@Id@GeneratedValue(generator = "nat")@GenericGenerator(name = "nat", strategy = "native")public int getId() {return id;}public void setId(int id) {this.id = id;}@Overridepublic String toString() {return "Order [id=" + id + ", price=" + price + ", getId()=" + getId() + ", getClass()=" + getClass()+ ", hashCode()=" + hashCode() + ", toString()=" + super.toString() + "]";}public int getPrice() {return price;}public void setPrice(int price) {this.price = price;}}