《Hibernate上课笔记》------class6------Hibernate实现一对多关联映射-阿里云开发者社区

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;
  }
  @Override
  public 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;
  }
  @Override
  public 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;
  }
  @Override
  public 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;
  }
  @Override
  public 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;
  }
  @Override
  public 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;
  }
  @Override
  public 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;
  }
}

《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）

2.数据库一对多关联

二：Hibernate实现单向一对多关联

1.xml配置实现

二：Hibernate双向一对多关联

1.使用xml文件方式完成配置

2.使用注解方式完成配置

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插件

《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）

2.数据库一对多关联

二：Hibernate实现单向一对多关联

1.xml配置实现

二：Hibernate双向一对多关联

1.使用xml文件方式完成配置

2.使用注解方式完成配置

热门文章

最新文章

相关电子书