How do you represent collections of Hibernate objects in a single POJO?

Question

Consider the following Hibernate mappings:

<hibernate-mapping package="org.example">
  <class name="Customer" table="CUSTOMER">
    <id name="customerId" column="customer_id"/>

    <bag name="itineraries" table="ITINERARY" inverse="true" cascade="all">
      <key column="customer_id"/>
      <one-to-many class="Itinerary"/>
    </bag>

    <bag name="hotels" table="HOTEL" inverse="true" cascade="all">
      <key column="customer_id"/>
      <one-to-many class="Hotel"/>
    </bag>
  </class>
</hibernate-mapping>

<hibernate-mapping package="org.example">
    <class name="Itinerary" table="ITINERARY">
      <many-to-one name="customer" column="customer_id" update="false" not-null="true"/>
      ...other properties...
    </class>
</hibernate-mapping>

<hibernate-mapping package="org.example">
    <class name="Hotel" table="HOTEL">
      <many-to-one name="customer" column="customer_id" update="false" not-null="true"/>
      ...other properties...
    </class>
</hibernate-mapping>

Now say you need to remove the CUSTOMER table. How would you refactor the mappings/model such that the Customer Java object continues to contain Lists of Itinerary and Hotel objects based on a customerId? Said Hotel and Itinerary objects still need to be managed by Hibernate.

The best I can come up with is the Customer object deferring to DAOs when callers request a List. Is there a cleaner approach that will still allow the Customer object to live in each Itinerary and Hotel object?

Answer 1

Once you remove the customer table, the customer object will not be managed by Hibernate anymore. If you still want to have a customer object containing Itinerary and Hotel, then that needs to be done programmatically. I am not sure if you are really looking for this.

One possible way of doing this is

1. Lets say you have a DAO with a method getCustomer(). This accepts a customer id.
2. This method fires two more queries to fetch lists of Itinerary and Hotel based on the customer id.
3. It creates a Customer object and sets the lists of Itinerary and Hotel into it and returns it and populated customer object.