具有共享主键的双向一对一关系的外键约束冲突

我试图用JPA在两个类之间创建一对一的关联,一个是父类,另一个是子类,使用一个生成器来确保它们具有相同的主键:

@Entity
public class TestFKParent {

    @Column(name="code", nullable=false)    
    @Id 
    private String code;

    @OneToOne(mappedBy="parent", targetEntity=TestFKChild.class, optional=false)    
    @org.hibernate.annotations.Cascade({CascadeType.ALL})
    @PrimaryKeyJoinColumn
    private TestFKChild child;

    // getters and setters
}

@Entity
public class TestFKChild {

    @Column(name="id", nullable=false)  
    @Id 
    @GeneratedValue(generator="MyGen")  
    @org.hibernate.annotations.GenericGenerator(name="MyGen",
            strategy="foreign",parameters = @Parameter(name = "property", value = "parent"))    
    private String ID;

    @OneToOne(targetEntity=TestFKParent.class, optional=false)  
    @org.hibernate.annotations.Cascade({})
    @PrimaryKeyJoinColumn
    private TestFKParent parent;

    // getters and setters
}

我用以下代码持久化对象:

public void testMerge() throws Exception
{
    TestFKParent parent = new TestFKParent();
    parent.setCode("foo");
    TestFKChild child = new TestFKChild();
    parent.setChild(child);
    child.setParent(parent);

    em.merge(parent);
}

com.sybase.jdbc3.jdbc.SybSQLException: Foreign key constraint violation occurred, dbname =  'MYDB', table name = 'TestFKChild', constraint name = 'FKE39B2A659CF5145B'

从日志来看,它似乎试图先持久化子项,但在这个TestFKChild表中,我在TestFKParent父项上有一个外键。

在JPA/Hibernate中,描述这种关系的正确方法是什么?