@Entity
@Table(name = "documents")
@Inheritance(strategy = InheritanceType.JOINED)
public class Document extends BaseBO {
    private Set<Binary> resources;
    ....

    /**
     * removes the binary from the document if it is part of it
     * @param binary the binary to be removed from the document
     */
    protected void removeResource(Binary binary){
        resources.remove(binary);
        binary.setParent(null);
    }

    /**
     * adds a resource to the document
     * @param binary the binary to be added to the document
     */
    protected void addResource(Binary binary){
        if ( getResources() == null )
            resources = new HashSet<Binary>(5);
        resources.add(binary);
        binary.setParent(this);
    }

    .....

    @OneToMany(cascade = CascadeType.ALL, mappedBy = "parent", targetEntity = Binary.class)
    public Set<Binary> getResources() {
        return resources;
    }

    public void setResources(Set<Binary> resources) {
        this.resources = resources;
    }

}

@Entity
@Table(name = "blobs")
@Inheritance(strategy = InheritanceType.JOINED)
public class Binary extends BaseBO {
    private Timestamp lastUpdate;
    ....
    private Document parent;
    .....

    @Column (nullable = false)
    public Timestamp getLastUpdate() {
        return lastUpdate;
    }

    protected void setLastUpdate(Timestamp lastUpdate) {
        this.lastUpdate = lastUpdate;
    }

    @ManyToOne
    @JoinColumn(name = "parent", nullable = false)
    public Document getParent() {
        return parent;
    }

    public void setParent(Document parent) {
        this.parent = parent;
    }

    /**
     * checks for the update of the default value, only one bean can be default one
     *
     * @param session the session for data modify
     * @return true if the process should fail
     * @throws org.hibernate.CallbackException
     *
     */
    @Override
    public boolean onSave(Session session) throws CallbackException {
        setLastUpdate(new Timestamp(System.currentTimeMillis()));
        return super.onSave(session);
    }

    /**
     * checks for the update of the default value, only one bean can be default one
     *
     * @param session the session for data modify
     * @return true if the process should fail
     * @throws org.hibernate.CallbackException
     *
     */
    @Override
    public boolean onUpdate(Session session) throws CallbackException {
        setLastUpdate(new Timestamp(System.currentTimeMillis()));
        return super.onUpdate(session);
    }
}

public void storeFile(String userId, String docAliasId, String fileAliasId, String fileName, String contentType,
                          InputStream inputStream)
            throws PersistenceException, IllegalArgumentException, IOException {
        Transaction tx = newTransaction();
      ....
            Document document = findByAlias(userId, docAliasId);
            if (document == null) {
                //now creating the file
                FileResource fileResource = new FileResource();
                document = initDocument(docAlias, registrator, fileResource, fileName, contentType, binaryAlias, inputStream);
                persist(document);
            } else {
       ....
                FileResource fileResource = (FileResource) query.uniqueResult();[b]//this class extends Binery[/b]
                if (fileResource == null) {
                    fileResource = new FileResource(); //now creating the file
                    fileResource.setId(UUID.randomUUID().toString());
                }
                fileResource.setFileName(fileName);
                fileResource.setContentType(contentType);
                fileResource.setAlias(binaryAlias);
                fileResource.setData(IOUtils.toByteArray(inputStream));
                document.addResource(fileResource);
                persist(document);
            }
            commit(tx);
        } catch (HibernateException e) {
            rollback(tx);
            throw new PersistenceException("can not store the document", e);
        } catch (IOException e) {
            rollback(tx);
            throw e;
        }
    }