Question

I am facing a problem with parent child type relations.
Hibernate docs say to add a “many-to-one” relation in child class to get value of foreign key from parent. But to make this relation work I have to add Invoice property in child class that introduce a circular inclusion of parent into child and breaks my serializer. Could somebody point where am I doing mistake?

Here is my code:

Invoice.java

public class Invoice implements Serializable {
  private Long id;
  private Date invDate;
  private String customer;
  private Set<InvoiceItem> items;
  ... getters/setters ...
}

InvoiceItem.java

public class InvoiceItem implements Serializable {
  private Long itemId;
  private long productId;
  private int quantity;
  private double price;
  private Invoice invoice; //???????
  ... getters/setters ...
}

Invoice.hbm.xml

<class name="Invoice" table="Invoices">
  <id name="id" column="ID" type="long">
    <generator class="native" />
  </id>
  <property name="invDate" type="timestamp" />
  <property name="customer" type="string" />

  <set name="items" inverse="true" cascade="all-delete-orphan">
    <key column="invoiceId" />
    <one-to-many class="InvoiceItem" />
  </set>
</class>

InvoiceItem.hbm.xml

<class name="InvoiceItem" table="InvoiceItems">
  <id name="itemId" type="long" column="id">
    <generator class="native" />
  </id>

  <property name="productId" type="long" />
  <property name="quantity" type="int" />
  <property name="price" type="double" />

<many-to-one name="invoiceId" class="Invoice" not-null="true"/> <!--????????-->
</class>

Answer 1

You don’t have to have a reference to Invoice in InvoiceItem if you remove the inverse=”true” attribute.
Hibernate will then create a separate mapping table rather than use a foreign key in the InvoiceItem table.

Remove the inverse attribute on the InvoiceItem set, and also remove the Invoice property from InvoiceItem, and the corresponding many-to-one in the mapping and you should get what you want.

Alternatively, you could mark the Invoice reference in InvoiceItem as transient, and handle populating the value during deserialization: iterate over the Set of Items in Invoice, and set the invoice property on each item to the owning invoice.