java - hibernate :对象以错误的顺序创建？

Question

我刚从 XML 映射切换到注释，不得不意识到我的序列化类不再起作用了!我希望你能帮我找出原因:)

我有一个 School 类，其中包含一个 Address

@Entity
@Table(name="schools")
    public class School {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name = "id")
    private Long id;

    @ManyToOne
    @JoinColumn(name="address_id", nullable=true)
    private Address address;
        ...
}

地址类:

@Entity
@Table(name="addresses")
public class Address {
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name = "id")
    private Long id;

    @Column(name="street", nullable=false, updatable=true)
    private String street;      // with nr
    ...
}

我尝试这样序列化:

sessionFactory = MyFactory.getSessionFactory();
            session = sessionFactory.openSession();

            Transaction tx = session.beginTransaction();

            School mbs = new School("interesting school");
            Address a = new Address("garden street 5","12345", "somewhere");
            mbs.setAddress(a);

            session.save(mbs);
            tx.commit();

这在以前对 XML 有效，但现在无效..

控制台上可见的第一个 Hibernate 查询操作是:Hibernate:插入学校(address_id，layout_id，name)值(？，？，？)

因此出现错误:ERROR: Column 'address_id' cannot be null

我该如何解决这个问题？

.

那些是表格:

CREATE TABLE schools(
    id INTEGER NOT NULL AUTO_INCREMENT,
    name CHAR(50),

    address_id INTEGER NOT NULL,
    layout_id INTEGER NOT NULL,

    CONSTRAINT fk_address FOREIGN KEY (address_id) REFERENCES addresses(id),
    CONSTRAINT fk_layout FOREIGN KEY (layout_id) REFERENCES layout_headers(id),

    PRIMARY KEY (id)
);
CREATE TABLE addresses(
    id INTEGER NOT NULL AUTO_INCREMENT,
    street CHAR(55),
    zip CHAR(6),
    city CHAR(60),

    CONSTRAINT addr_pk PRIMARY KEY (id)
);

在我的 hibernte.cfg.xml 中我有以下内容:

<hibernate-configuration>
    <session-factory>
     ...
        <mapping class="creator.models.school.Address" />
        <mapping class="creator.models.school.Report" />
        <mapping class="creator.models.school.School" />
        <mapping class="creator.models.school.SchoolClass" />
        ...
    </session-factory>
</hibernate-configuration>

Answer 1

您应该在 School 类的 address 字段上指定 @ManyToOne 注解的 cascade 属性，以便在保存地址之前学校。例如，CascadeType.ALL