Composite Primary Key Hibernate and Java Implementation

Question

I have defined a very simple database as follow :

I'm using the hibernate plug-in to generate the different classes, including the one-to-many relationship between customer and order. i made this relationship as an identifying relationship as an order could not exist if not linked to a customer.

I have the three following classes :

=> Class Customer

private int idCustomer;
private String name;
private Set<Order> orders = new HashSet<Order>(0);

public Customer() {
}

public Customer(int idCustomer) {
    this.idCustomer = idCustomer;
}

public Customer(int idCustomer, String name, Set<Order> orders) {
    this.idCustomer = idCustomer;
    this.name = name;
    this.orders = orders;
}

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "idCustomer", unique = true, nullable = false)
public int getIdCustomer() {
    return this.idCustomer;
}

public void setIdCustomer(int idCustomer) {
    this.idCustomer = idCustomer;
}

@Column(name = "name", length = 45)
public String getName() {
    return this.name;
}

public void setName(String name) {
    this.name = name;
}

@OneToMany(fetch = FetchType.LAZY, mappedBy = "customer")
public Set<Order> getOrders() {
    return this.orders;
}

public void setOrders(Set<Order> orders) {
    this.orders = orders;
}

=> Class Order :

private OrderId id;
private Customer customer;
private String quantity;
private Float price;

public Order() {
}

public Order(OrderId id, Customer customer) {
    this.id = id;
    this.customer = customer;
}

public Order(OrderId id, Customer customer, String quantity, Float price) {
    this.id = id;
    this.customer = customer;
    this.quantity = quantity;
    this.price = price;
}

@EmbeddedId
@AttributeOverrides({
        @AttributeOverride(name = "idOrder", column = @Column(name = "idOrder", nullable = false)),
        @AttributeOverride(name = "customerIdCustomer", column = @Column(name = "Customer_idCustomer", nullable = false)) })
public OrderId getId() {
    return this.id;
}

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

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "Customer_idCustomer", nullable = false, insertable = false, updatable = false)
public Customer getCustomer() {
    return this.customer;
}

public void setCustomer(Customer customer) {
    this.customer = customer;
}

@Column(name = "quantity", length = 45)
public String getQuantity() {
    return this.quantity;
}

public void setQuantity(String quantity) {
    this.quantity = quantity;
}

@Column(name = "price", precision = 12, scale = 0)
public Float getPrice() {
    return this.price;
}

public void setPrice(Float price) {
    this.price = price;
}

=> Class OrderId

private int idOrder;
private int customerIdCustomer;

public OrderId() {
}

public OrderId(int idOrder, int customerIdCustomer) {
    this.idOrder = idOrder;
    this.customerIdCustomer = customerIdCustomer;
}

@Column(name = "idOrder", nullable = false)
public int getIdOrder() {
    return this.idOrder;
}

public void setIdOrder(int idOrder) {
    this.idOrder = idOrder;
}

@Column(name = "Customer_idCustomer", nullable = false)
public int getCustomerIdCustomer() {
    return this.customerIdCustomer;
}

public void setCustomerIdCustomer(int customerIdCustomer) {
    this.customerIdCustomer = customerIdCustomer;
}

public boolean equals(Object other) {
    if ((this == other))
        return true;
    if ((other == null))
        return false;
    if (!(other instanceof OrderId))
        return false;
    OrderId castOther = (OrderId) other;

    return (this.getIdOrder() == castOther.getIdOrder())
            && (this.getCustomerIdCustomer() == castOther
                    .getCustomerIdCustomer());
}

public int hashCode() {
    int result = 17;

    result = 37 * result + this.getIdOrder();
    result = 37 * result + this.getCustomerIdCustomer();
    return result;
}

I then have my main class :

public static void main(String[] args) {
    Customer customer = new Customer();
    customer.setName("John Doe");
    CustomerDAO.save(customer);

    Order order = new Order();
    order.setQuantity(10);
    order.setPrice(100);
    order.setCustomer(customer);

    OrderDAO.save(order);

}

Please note that my DAO objects are doing nothing fancy... Just the usual HibernateUtil implementation of getting the session and finally call the 'save' method. My Problem is the following. I have never dealt before with composite key... Excuse me for my stupid question in advance. I don't want to deal manually with the different ids and primary keys. For the Cutomer class, it is not a problem since I set up a strategy that will automatically create the id when saving in database. For the Order class, I don't want to deal with that as well. But since the key is composite, Hibernate generates an identifierGenerationExeption when trying to save this object in DB... What I would have liked is the following => an Order id generated automatically and since I setup the customer in the order Object, I would have expect hibernate to link the customer id to the one in the composite key... What is the correct way of doing this thing ?

Thanks

Answer 1

Using composite keys is discouraged and should only be used when forced to do it (say: legacy database). I think that you just should make the Customer_id in the Order not null . There is a simple, regular id for the order ( idOrder ) and everything should be straight forward.

Answer 2

Why do you include the customer ID foreign key in the primary key of your Order entity? Its primary key should be idOrder . Customer_idCustomer should be a foreign key, and should not be part of the ID of Order.