How to reference a parent's id in a child's id with JPA/Hibernate?

Question

Given a table (MY_TABLE_A) that automatically increments it's id upon each new insertion (i.e. the first record in the database has it's ID attribute 1, the second record has it's ID attribute set to 2, the third record has it's ID attribute set to 3). The ID I am talking about is the table's primary key.

I also have another table (MY_TABLE_B) that reference's the original table's primary key. When I try to persist both to my Oracle database, I get a org.hibernate.id.IdentifierGenerationException: ids for this class must be manually assigned before calling save()

What I want to accomplish: Whenever I persist an object to MY_TABLE_A, I want MY_TABLE_B to insert an object with the same ID that MY_TABLE_A gets since it's auto incremented (wouldn't know what the next value is until it's inserted). To clarify, one id in Table A should have only one matching ID in Table B

Here are some snippets of my code below:

FirstClass:

@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
}

---

SecondClass:

@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
}

---

Service Layer snippet where I insert new entries for each in Oracle:

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

---

Details on insert() for firstClassService:

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

---

insert() for secondClassService:

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

UPDATE

What FirstClass looks like now:

@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;
}

---

SecondClass:

@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

Mappings should be as below:

@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;
}

With the Cascade option set then you you will only need to make the call to save firstClass: the associated secondClass will be persisted automatically - assuming you set both sides of the relationhsip in your in-memory model i.e.

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

Answer 2

Add @GeneratedValue(strategy=GenerationType.IDENTITY) to the id of second class.

@Id
@Column(name = "MY_ID")
@GeneratedValue(strategy=GenerationType.IDENTITY)
private Integer myId;
// more variables, getters/setters

Answer 3

From your description it seems like you have a ManytoOne relation, as your table B references table A, then it's logic to say A has a list of Bs somewhat, so why not take advantage of what ORM actually is and why not keep a reference in A such as:

@OneToMany(mappedBy="aa")
private List<B> bs;

and use the annotation in the other entity:

@ManyToOne
@JoinColumn(name = "myId" , referencedColumnName = "id")
private A aa;

That in combination to what Jens suggested, see OracleDialect does not support identity key generation