本文共 4216 字，大约阅读时间需要 14 分钟。

无连接表的N-1关联

多个Employee关联一个Department。

Employee实体（N端）:

package com.ydoing.hibernate2;import javax.persistence.CascadeType;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.FetchType;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.JoinTable;import javax.persistence.ManyToOne;import javax.persistence.Table;@Entity@Table(name = "employee_inf")public class Employee {    @Id    @Column(name = "employee_id")    @GeneratedValue(strategy = GenerationType.IDENTITY)    private Integer id;    // N-1单向关联    @ManyToOne(targetEntity = Department.class, cascade = CascadeType.ALL, fetch = FetchType.LAZY)    @JoinColumn(name = "department_id", nullable = false)    private Department department;      ....省略get和set方法...

Department实体（1端）:

package com.ydoing.hibernate2;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.Table;@Entity@Table(name = "department_inf")public class Department {
       @Id    @Column(name = "department_id")    @GeneratedValue(strategy = GenerationType.IDENTITY)    private Integer id;    private String name;      ....省略get和set方法...

测试：

package com.ydoing.hibernate2;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.Transaction;import org.hibernate.boot.registry.StandardServiceRegistryBuilder;import org.hibernate.cfg.Configuration;import org.hibernate.service.ServiceRegistry;import org.junit.BeforeClass;import org.junit.Test;public class Main {    private static Session session;    @BeforeClass    public static void init() {        Configuration conf = new Configuration();        conf.configure();        ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(conf.getProperties())                .build();        SessionFactory factory = conf.buildSessionFactory(serviceRegistry);        session = factory.openSession();    }    @Test    public void test() {        Employee emp = new Employee();        emp.setName("Jack");        emp.setAge(20);        emp.setDepartment(new Department("dev"));        Transaction tx = session.getTransaction();        tx.begin();        session.save(emp);        tx.commit();        session.close();    }}

Console输出：

Hibernate:     insert     into        department_inf        (name)     values        (?)Hibernate:     insert     into        employee_inf        (age, department_id, name)     values        (?, ?, ?)

从以上输出不能看出，Hibernate先插入主表address_inf，然后再持久化从表employee_inf。并没有连接表生成。但是employee_inf多出来外键列department_id。

数据表：

有连接表的N-1关联

还是用以上的列子，修改Employee类：

package com.ydoing.hibernate2;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.JoinColumn;import javax.persistence.JoinTable;import javax.persistence.ManyToOne;import javax.persistence.Table;@Entity@Table(name = "employee_inf")public class Employee {
       @Id    @Column(name = "person_id")    @GeneratedValue(strategy = GenerationType.IDENTITY)    private Integer id;    //N-1单向有连接表关联    @ManyToOne(targetEntity = Department.class, cascade = CascadeType.ALL)    // @JoinColumn(name = "department_id", nullable = false)    @JoinTable(name = "employee_department", // 连接表名    joinColumns = @JoinColumn(name = "person_id", referencedColumnName = "person_id", unique = true), inverseJoinColumns = @JoinColumn(name = "department_id", referencedColumnName = "department_id"))    private Department department;      ....省略get和set方法...

Console输出：

Hibernate:     insert     into        department_inf        (name)     values        (?)Hibernate:     insert     into        employee_inf        (age, name)     values        (?, ?)Hibernate:     insert     into        employee_department        (department_id, person_id)     values        (?, ?)

从输出可以看出，Hiberate主动创建了employee_department表，并把employee_inf和department_inf两个表关联起来，还有这两个表都没有增加外键列。

数据表：