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Re: [eclipselink-users] How to map cyclic foreign key references with not-null?
Because of your constraints, you cannot insert a row into FOO unless it can reference an existing row in BAR but you cannot insert into BAR until it can reference an existing row in FOO. So there is no way to insert a row in either table without turning a constraint off or delaying constraint processing on your database until the transaction is done. If you can't delay constraint processing on the database until the transaction commits, then I'd recommend you remove the not-null constraints and have application logic prevent it from being set to null. 
Best Regards,
Chris


On 28/07/2011 10:34 AM, janne postilista wrote:

How do I map the following scenario:

TABLE FOO (
  ID NUMBER(10) PRIMARY KEY NOT NULL,
  BAR_ID NUMBER(10) FOREIGN KEY NOT NULL
);

TABLE BAR (
  ID NUMBER(10) PRIMARY KEY NOT NULL,
  FOO_ID NUMBER(10) FOREIGN KEY NOT NULL
);

ids from sequences SEQ_FOO and SEQ_BAR.

When I try to persist/merge this kind of dual object I always get:

Caused by: org.h2.jdbc.JdbcSQLException: NULL not allowed for column
"BAR_ID"; SQL statement:
INSERT INTO FOO (ID, BAR_ID) VALUES (?, ?) [23502-154]
        at org.h2.message.DbException.getJdbcSQLException(DbException.java:327)
        at org.h2.message.DbException.get(DbException.java:167)
        at org.h2.message.DbException.get(DbException.java:144)
        at org.h2.table.Column.validateConvertUpdateSequence(Column.java:297)
        at org.h2.table.Table.validateConvertUpdateSequence(Table.java:669)

My mappings:

@Entity
@Table(name = "FOO")
public class Foo {

    @Id
    @Column(nullable = false)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "FOO_GEN")
    @SequenceGenerator(name = "FOO_GEN", sequenceName = "SEQ_FOO",
allocationSize = 1)
    private Long id;

    @OneToOne
    @JoinColumn(name = "BAR_ID")
    private Bar bar;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public Bar getBar() {
        return bar;
    }

    public void setBar(Bar bar) {
        this.bar = bar;
    }


}



@Entity
@Table(name = "BAR")
public class Bar {

    @Id
    @Column(nullable = false)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "BAR_GEN")
    @SequenceGenerator(name = "BAR_GEN", sequenceName = "SEQ_BAR",
allocationSize = 1)
    private Long id;

    @OneToOne
    @JoinColumn(name = "FOO_ID")
    private Foo foo;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public Foo getFoo() {
        return foo;
    }

    public void setFoo(Foo foo) {
        this.foo = foo;
    }

}

I get the same result using ManyToOne relationships. I have also tried
a combination with Foo having ManyToOne Bar and Bar having OneToOne
Foo.

Actual relationships are a) unidirectional 1:n mapping and b)
unidirectional 1:1 mapping.
- n Foo objects all point to same Bar. Bar does not need to know the
collection of n Foo objects pointing to it
- each Bar points to a single Foo.
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