Hibernate注解开发之关联映射的注解

回顾

1. 一对一单向外键关联

Students04

@Entity
public class Students04 implements Serializable {

    @Id //设置为主键
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int sid;
    @OneToOne(cascade = CascadeType.ALL)//指定被控类, 默认是全级联
    @JoinColumn(name = "pid", unique = true)//name指定被控类(IdCard类)的主键, unique说明该键是唯一的
    private IdCard card;
    private String gender; //性别
    private Date birthday; //出生日期
    private String major; //专业  ... 构造方法和settergetter方法自行补充 ...}

IdCard

@Entity
public class IdCard {

    @Id
    @GeneratedValue(generator = "pid")
    @GenericGenerator(name = "pid", strategy = "assigned")
    @Column(length = 18)
    private String pid;  //身份证号码
    private String sname;  //学生姓名  ... 构造方法和settergetter方法自行补充 ...}

配置文件

<mapping class="com.idea.hibernate.oto_fk.Students04"/>
<mapping class="com.idea.hibernate.oto_fk.IdCard"/>

测试(保存主表对象之前, 应该先保存外键对象)

@Test
public void addStudents04(){
    Configuration configuration = new Configuration().configure();
    SessionFactory sessionFactory = createSessionFactory(configuration);
    Session session = sessionFactory.getCurrentSession();
    Transaction tx = session.beginTransaction();
    IdCard card = new IdCard("1234567890123456", "王五");
    Students04 students04 = new Students04(card, "男", new Date(), "Java开发");
    session.save(card);
    session.save(students04);
    tx.commit();
}

/**
 * 建表策略
 */
private SessionFactory createSessionFactory(Configuration configuration){
    //创建服务注册对象
    StandardServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();
    //生成SssionFactory
    SessionFactory  sessionFactory = configuration.buildSessionFactory(serviceRegistry);
    //返回配置对象
    return sessionFactory;
}

ps: 同一个实体类中注解要不全写在属性上, 要不全写在getXxx方法上, 不可混用.

2. 一对一双向外键关联

特点: 你中有我, 我中有你

主控方的写法跟一对一单向关联相同, 区别在于被控方(IdCard)

双向关联, 必须设置mappedBy属性, 交给主控方去控制.

IdCard02

@Entity
public class IdCard02 {

    @Id
    @GeneratedValue(generator = "pid")
    @GenericGenerator(name = "pid", strategy = "assigned")
    @Column(length = 18)
    private String pid;  //身份证号码
    private String sname;  //学生姓名
    @OneToOne(mappedBy = "card")  //指定主控方(Students05)中的属性
    private Students05 students05;  ... 构造方法和settergetter方法自行补充 ...}

其他部分都相同.

3. 一对一双向外键联合主键

① 创建主键类StudentsPK

② 主键类上注解@Embeddable

@Embeddable
public class StudentsPK implements Serializable {

    private static final long serialVersionUID = 6632444697825110476L;
    @Column(length = 18)
    private String id;  //身份证号
    @Column(length = 8)
    private String sid;  //学号  ...}

③ 在实体类引入该主键类的属性, 并在属性上使用注解@EmbeddedId

详细移步Hibernate注解开发之属性级别的注解

4. 一对多单向外键关联

一的一方持有多的一方的集合, 如一个班级有多个学生(一对多)

Students07

@Entity
public class Students07 implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int sid;
    private String sname;
    private String gender;
    private String major;
    private Date birthday; ...}

ClassRoom01

@Entity
public class ClassRoom01 {

    @Id
    @GeneratedValue(generator = "cid")
    @GenericGenerator(name = "cid", strategy = "assigned")
    @Column(length = 4)
    private String cid;
    private String cname;
    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)  //多的一方使用急加载, 一的一方使用懒加载
    @JoinColumn(name = "CID")
    private Set<Students07> stus;  //一的一方持有多的一方的集合  ...}

5. 一对多双向外键关联

班级类和单向的配置相同, 只是在学生类中多加入班级类的引用

Students08

@Entity
public class Students08 implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int sid;
    private String sname;
    private String gender;
    private String major;
    private Date birthday;
    @ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.EAGER)  //多的一方需要设为急加载
    @JoinColumn(name = "CID")
    private ClassRoom02 classRoom02;  //多的一方持有一的一方的引用  ...}

6. 多对多单向外键关联

① 学生和教师的对应关系为多对多关联关系

② 学生表持有教师表的集合

③ 创建中间表

Students09

@Entity
public class Students09 implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int sid;
    private String sname;
    private String gender;
    private String major;
    private Date birthday;
    @ManyToMany
    @JoinTable(
            name = "teachers_students",  //中间表的名称
            joinColumns = {@JoinColumn(name = "SID")},  //中间表外键关联字段的名称
            inverseJoinColumns = {@JoinColumn(name = "TID")}  //中间表外键关联字段的名称
    )
    private Set<Teachers> teachers;  //学生持有教师的集合  ...}

Teachers

@Entity
public class Teachers {

    @Id
    @GeneratedValue(generator = "tid")
    @GenericGenerator(name = "tid", strategy = "assigned")
    @Column(length = 4)
    private String tid;  //教师的编号
    private String tname;  //教师的姓名 ...}

7. 多对多双向外键关联

双方都持有对方的集合, 涉及到主控方和被控方, 需要将控制权交给主控方

@Entity
public class Teachers01 {

    @Id
    @GeneratedValue(generator = "tid")
    @GenericGenerator(name = "tid", strategy = "assigned")
    @Column(length = 4)
    private String tid;  //教师的编号
    private String tname;  //教师的姓名
    @ManyToMany(mappedBy = "teachers")  //将主控权给学生方, teachers是学生类中的属性
    private Set<Students10> stus;   ...}

学生类跟测试同上

Hibernate注解开发之关联映射的注解

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