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[Hibernate] - Annotations - Many To Many
Hibernate annotation 多对多:
下面测试例子会自动生成一张表:card,这张是bank和user表的映射表。里头是bank_id和user_id两个组合字段。
如果想在这张映射表中加入额外的字段,那么hibernate似乎无法做到。因为这需要把多对多写成两个一对多的关系。事实上这样加额外字段到映射表,好像也是违反了DBMS的设计原则。
hibernate.cfg.xml
<?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://127.0.0.1/testdb</property> <property name="connection.username">root</property> <property name="connection.password"></property> <!-- JDBC connection pool (use the built-in) --> <property name="connection.pool_size">1</property> <!-- SQL dialect --> <property name="dialect">org.hibernate.dialect.MySQL5Dialect</property> <!-- Enable Hibernate‘s automatic session context management --> <property name="current_session_context_class">thread</property> <!-- Disable the second-level cache --> <property name="cache.provider_class">org.hibernate.cache.internal.NoCacheProvider</property> <!-- Echo all executed SQL to stdout --> <property name="show_sql">true</property> <!-- Drop and re-create the database schema on startup --> <property name="hbm2ddl.auto">update</property> <mapping class="com.my.bean.User"/> <mapping class="com.my.bean.Bank"/> </session-factory></hibernate-configuration>
HibernateUtil.java
package com.my.dao.util;import org.hibernate.SessionFactory;import org.hibernate.boot.registry.StandardServiceRegistryBuilder;import org.hibernate.cfg.Configuration;public class HibernateUtil { private static final SessionFactory sessionFactory = buildSessionFactory(); private static SessionFactory buildSessionFactory() { try { // Create the SessionFactory from hibernate.cfg.xml Configuration configuration = new Configuration(); return configuration.configure().buildSessionFactory( new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build()); } catch (Throwable ex) { // Make sure you log the exception, as it might be swallowed System.err.println("Initial SessionFactory creation failed." + ex); throw new ExceptionInInitializerError(ex); } } public static SessionFactory getSessionFactory() { return sessionFactory; } }
Java Beans:
package com.my.bean;import java.util.Date;import java.util.HashSet;import java.util.Set;import javax.persistence.CascadeType;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.JoinTable;import javax.persistence.ManyToMany;import javax.persistence.Table;@Entity@Table(name="user")public class User { @Id @GeneratedValue @Column(name="user_id", nullable=false) private long userID; @Column(name="user_name", length=100, nullable=false) private String userName; @Column(name="create_time", nullable=false) private Date createTime; @ManyToMany(cascade=CascadeType.ALL) @JoinTable(name="card", joinColumns={@JoinColumn(name="user_id")}, inverseJoinColumns={@JoinColumn(name="bank_id")}) private Set<Bank> banks = new HashSet<Bank>(); public long getUserID() { return userID; } public void setUserID(long userID) { this.userID = userID; } public String getUserName() { return userName; } public void setUserName(String userName) { this.userName = userName; } public Date getCreateTime() { return createTime; } public void setCreateTime(Date createTime) { this.createTime = createTime; } public Set<Bank> getBanks() { return banks; } public void setBanks(Set<Bank> banks) { this.banks = banks; }}
package com.my.bean;import java.util.HashSet;import java.util.Set;import javax.persistence.CascadeType;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.ManyToMany;import javax.persistence.Table;import org.hibernate.annotations.Cascade;@Entity@Table(name="bank")public class Bank { @Id @GeneratedValue(strategy=GenerationType.IDENTITY) @Column(name="bank_id") private long bankID; @Column(name="bank_name", length=100, nullable=false) private String BankName; @ManyToMany(mappedBy="banks", cascade={CascadeType.ALL}) private Set<User> users = new HashSet<User>(); public long getBankID() { return bankID; } public void setBankID(long bankID) { this.bankID = bankID; } public String getBankName() { return BankName; } public void setBankName(String bankName) { BankName = bankName; } public Set<User> getUsers() { return users; } public void setUsers(Set<User> users) { this.users = users; }}
测试:
package com.my.init;import java.util.Date;import org.hibernate.Session;import org.hibernate.Transaction;import com.my.bean.Bank;import com.my.bean.User;import com.my.dao.util.HibernateUtil;public class Test { public static void main(String[] args) { Session session = HibernateUtil.getSessionFactory().openSession(); Transaction tx = session.beginTransaction(); try { //------------------------------------------------------- // add user //------------------------------------------------------- User user = new User(); user.setUserName("Robin"); user.setCreateTime(new Date()); //------------------------------------------------------- // add bank //------------------------------------------------------- Bank bankBCC = new Bank(); bankBCC.setBankName("BCC"); Bank bankCBC = new Bank(); bankCBC.setBankName("CBC"); //------------------------------------------------------- // set relcationship //------------------------------------------------------- user.getBanks().add(bankBCC); user.getBanks().add(bankCBC); //------------------------------------------------------- // save //------------------------------------------------------- session.save(user); session.save(bankBCC); session.save(bankCBC); //------------------------------------------------------- // remove data //------------------------------------------------------- session.delete(user); tx.commit(); } catch (Exception e) { tx.rollback(); e.printStackTrace(); } session.close(); }}
参考文档:
http://viralpatel.net/blogs/hibernate-many-to-many-annotation-mapping-tutorial/
[Hibernate] - Annotations - Many To Many
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