java - 如何使用 JPA/Hibernate 在 child 的 id 中引用 parent 的 id？

Question

给定一个表( MY_TABLE_A )，它在每次新插入时自动递增其 id(即数据库中的第一条记录的 ID 属性为 1，第二条记录的 ID 属性设置为 2，第三条记录的 ID 属性为 2) ID 属性设置为 3)。我所说的 ID 是表的主键。

我还有另一个表 ( MY_TABLE_B )，它引用原始表的主键。当我尝试将两者持久保存到我的 Oracle 数据库时，我得到 org.hibernate.id.IdentifierGenerationException: ids for this class must be manually assigned before calling save()

我想要完成的任务:每当我将一个对象持久化到 MY_TABLE_A 时，我要MY_TABLE_B插入一个与 MY_TABLE_A 具有相同 ID 的对象获取，因为它是自动递增的(在插入之前不知道下一个值是什么)。澄清一下，表 A 中的一个 id 在表 B 中应该只有一个匹配的 ID

下面是我的一些代码片段:

头等舱:

@Entity
@Table(name = "MY_SCHEMA.MY_TABLE_A")
@Component
public class FirstClass implements Serializable {

    @Id
    @SequenceGenerator(name = "MY_SEQ", sequenceName = "MY_SCHEMA.MY_SEQ", allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "MY_SEQ")
    @Column(name = "MY_ID")
    private Integer myId;
    // more variables, getters/setters
}

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二等:

@Entity
@Table(name = "MY_SCHEMA.MY_TABLE_B")
@SecondaryTable(name = "MY_SCHEMA.MY_TABLE_A", pkJoinColumns = @PrimaryKeyJoinColumn(name = "MY_ID", referencedColumnName = "MY_ID"))
@Component
public class SecondClass {

    @Id
    @Column(name = "MY_ID")
    private Integer myId;
    // more variables, getters/setters
}

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服务层片段，我在 Oracle 中为每个服务层插入新条目:

firstClassService.insert();
secondClassService.insert();

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详细信息insert()对于头等舱服务:

public void insert() {
        FirstClass obj = new FirstClass();
        getCurrentSession().persist(obj);
}

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insert()对于第二类服务:

public void insert() {
        SecondClass obj = new SecondClass();
        getCurrentSession().persist(obj);
}

更新

FirstClass 现在的样子:

@Entity
@Table(name = "MY_SCHEMA.MY_TABLE_A")
@Component
public class FirstClass implements Serializable {

    @Id
    @SequenceGenerator(name = "MY_SEQ", sequenceName = "MY_SCHEMA.MY_SEQ", allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "MY_SEQ")
    @Column(name = "MY_ID")
    @OneToOne(mappedBy = "myId")
    private Integer myId;
}

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二等:

@Entity
@Table(name = "MY_SCHEMA.MY_TABLE_B")
@SecondaryTable(name = "MY_SCHEMA.MY_TABLE_B", pkJoinColumns = @PrimaryKeyJoinColumn(name = "MY_ID", referencedColumnName = "MY_ID"))
@Component
public class SecondClass implements Serializable {

    @Id
    @JoinColumn(name = "MY_ID", referencedColumnName = "MY_ID")
    @OneToOne
    private Integer restRequestId;
}

Answer 1

映射应如下所示:

@Entity
@Table(name = "MY_SCHEMA.MY_TABLE_A")
@Component
public class FirstClass implements Serializable {

    @Id
    @SequenceGenerator(name = "MY_SEQ", sequenceName = "MY_SCHEMA.MY_SEQ", allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "MY_SEQ")
    @Column(name = "MY_ID")
    private Long myId;

    @OneToOne(mappedBy = "firstClass", cascade = CascadeType.ALL)
    private SecondClass secondClass;
}

@Entity
@Table(name = "MY_SCHEMA.MY_TABLE_B")
@Component
public class SecondClass implements Serializable {

    @Id
    @JoinColumn(name = "MY_ID", referencedColumnName = "MY_ID")
    @OneToOne
    private FirstClass firstClass;
}

设置级联选项后，您只需调用保存firstClass:关联的secondClass将自动保留 - 假设您在内存模型中设置了关系的两侧，即

firstClass.setSecondClass(secondClass);
secondClass.setFirstClass(firstClass);