JPA related entities persist

Question

I've designed some tables for my application where I've placed something like that:

product                            productversion
---                                ---
productId                          productVersionId
productVersionId (ref)             productId (ref)
name                               length
                                       height

where we have relation one to many . I just need some base product with parameters which can change and versioned parameters so I can watch it's history. Now... I have problem with Persisting those objects. I've tried multiple ways, this is oldest one:

Product p = new Product();
p.name = "some name";
Productversion pv = new Productversion();
pv.length = 10;
pv.height = 20;
p.productversionId = pv;

But while trying to persist this object I've getting error that productId cannot be null and it refers to field productId inside Productversion object. How can I do this?

[update] Some more information about my problem:

public class Product implements Serializable {
    @JoinColumn(name = "productversionId", referencedColumnName = "productversionId")
    @ManyToOne(optional = true, cascade = CascadeType.PERSIST)
    private Productversion productversionId;

    @OneToMany(cascade = CascadeType.ALL, mappedBy = "productId")
    private Collection<Productversion> productversionCollection;

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "ProductId")
    private Integer productId;

    @Basic(optional = false)
    @NotNull
    @Size(min = 1, max = 255)
    @Column(name = "Name")
    private String name = null;

    // well I believe construct and getter/setter not important now

And second Entity:

public class Productversion implements Serializable {
    @OneToMany(cascade = CascadeType.ALL, mappedBy = "productversionId")
    private Collection<Productiondata> productiondataCollection;
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "productversionId")
    private Integer productversionId;
    @Basic(optional = false)
    @NotNull
    @Column(name = "parameter")
    private float weight;

And the way I create new object (just have no idea how can I do this):

public Product getNewProduct() {
    if (newProduct == null) {
        this.newProduct = new Product();
        Productversion pv = new Productversion();
        pv.setProductId(newProduct);
        newProduct.setProductversionId(pv);
    }
    return newProduct;
}

And the way I'm trying to persist object:

public Boolean addEntry(Product productData) {
    Boolean status = false;
    DbConnector dc = new DbConnector();
    EntityManager em = dc.getEntityManager();

    try {
        EntityTransaction et = em.getTransaction();
        et.begin();
        em.persist(productData);
        et.commit();
        status = true;
    } finally {
        em.close();
    }
    return status;
}

Answer 1

Seems like you missing on the set for the id field in your Product object.

Product p = new Product(); 
p.id = 1;   <<<<<<-------------------
p.name = "some name";