Hibernate03-基础-JPA

Hibernate03-基础-JPA

1.hibernate和JPA的关系

1. jpa中定义了操作数据库的接口，hibernate是JPA的一种实现。
2. JPA的其他两种实现TopLink和OpenJPA。

2.JPA注解开发

1. 实体类。

@Data
@Entity
@Table(name = "tb_customer")
public class Customer {

    @Id
    @Column(name = "id")
    // GenerationType.IDENTITY，使用数据库的底层策略。
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(name = "name")
    private String name;
}

2. hibernate.cfg.xml配置。

<mapping class="com.my.jpa.test.Customer" />

3. 测试。

@Test
public void test01() {
    Customer customer = new Customer();
    customer.setName("jpa");
    session.save(customer);
}

4. @Transient，指定字段为临时字段，不需要映射到数据库。

// @Transient，临时字段，不需要映射到数据库。
// 如果没有加@Transient，会在启动时为表添加address临时字段。
@Transient
@Column(name = "address")
private String address;

3.JPA的四种主键策略

1. GenerationType.IDENTITY，利用数据库的自增长，适用于MySQL数据库。
2. GenerationType.SEQUENCE，利用数据库的序列机制，适合Oracle。
3. GenerationType.TABLE，利用JPA生成hibernate_sequences表维护主键值。
4. GenerationType.AUTO，自动选择策略，会利用JPA生成hibernate_sequences表维护主键值。

4.JPA对象关系映射-一对多

1. 实体类，一个Person多个Order。

@Data
@Setter
@Entity
@Table(name = "tb_person")
public class Person {

    @Id
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(name = "name")
    private String name;

    /**
     * mappedBy = "order"，Order中保存Person属性的字段名称
     */
    @OneToMany(targetEntity = Order.class, mappedBy = "person")
    private Set<Order> orders = new HashSet<>();
}

@Data
@Setter
@Entity
@Table(name = "tb_order")
public class Order {

    @Id
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(name = "orderNo")
    private String orderNo;

    /**
     * @JoinColumn(name = "person_id")，多方表中外键字段。
     */
    @JoinColumn(name = "person_id")
    @ManyToOne(targetEntity = Person.class)
    private Person person;
}

2. 测试insert。

@Test
public void test01() {
    Person person01 = new Person();
    person01.setName("tom");

    Person person02 = new Person();
    person02.setName("alice");

    Order o01 = new Order();
    o01.setOrderNo("AA01");

    Order o02 = new Order();
    o02.setOrderNo("BB02");

    o01.setPerson(person01);
    o02.setPerson(person01);

    session.save(person01);
    session.save(person02);
    session.save(o01);
    session.save(o02);
}

5.JPA对象关系映射-多对多

1. Java实体类，User和Role。

@Getter
@Setter
@Entity
@Table(name = "tb_user")
public class User {

    @Id
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    @Column(name = "name")
    private String name;

    @ManyToMany(targetEntity = Role.class)
    // name = "tb_user_role"，中间表为tb_user_role
    // joinColumns，当前方关联的列。
    // inverseJoinColumns，对方关联的列。
    @JoinTable(name = "tb_user_role",
            joinColumns = @JoinColumn(name = "user_id"),
            inverseJoinColumns = @JoinColumn(name = "role_id"))
    private Set<Role> roles = new HashSet<>();
}

@Getter
@Setter
@Entity
@Table(name = "tb_role")
public class Role {

    @Id
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    @Column(name = "name")
    private String name;

    @ManyToMany(targetEntity = User.class, mappedBy = "roles")
    private Set<User> users = new HashSet<>();
}

2. 测试代码。

@Test
public void test01() {
    User user01 = new User();
    user01.setName("tom");

    User user02 = new User();
    user02.setName("alice");

    Role role01 = new Role();
    role01.setName("A");

    Role role02 = new Role();
    role02.setName("B");

    // 只在User方维护关系即可
    user01.getRoles().add(role01);
    //role01.getUsers().add(user01);

    user02.getRoles().add(role01);
    //role02.getUsers().add(user02);


    session.save(user01);
    session.save(user02);
    session.save(role01);
    session.save(role02);
}

6.JAP对象映射-一对一

1. Java实体类。

@Getter
@Setter
@Entity
@Table(name = "tb_student")
public class Student {

    @Id
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(name = "name")
    private String name;

    @OneToOne(mappedBy = "student")
    private Card card;
}

@Getter
@Setter
@Entity
@Table(name = "tb_card")
public class Card {

    @Id
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(name = "card_no")
    private String cardNo;

    @OneToOne
    // 会在tb_card表中创建student_id列，用户映射tb_student的id，所以由Card维护外键关系。
    @JoinColumn(name = "student_id")
    private Student student;
}

2. 测试类。

@Test
public void test01() {
    Student student = new Student();
    student.setName("tom");

    Card card = new Card();
    card.setCardNo("A001");

    //
    card.setStudent(student);

    session.save(student);
    session.save(card);
}