Question

I am having a problem with mapping a entity that contains a list (or map). I’ve tried various combinations of annotations but the two variations that work the ‘best’ both have this behavior. If the parent-object has, for example, 3 child objects, the parent object is retrieved three times.

My Code

In my case i have an UserOrder object that contains pairs of Products with a count. The datastructure looks like this

@Entity
public class UserOrder{ 
    /* 
     * VARIATION 1 
     * I did actually vary some of these annotions, not all are necessary. 
     * I believe the @CollectionTable is the key here
     */
    @ElementCollection(fetch = FetchType.EAGER)
    @CollectionTable
    @Column
    @Embedded
    private List<ProductCount> products;

    /*
     * VARIATION 2
     */
    @ElementCollection(fetch = FetchType.EAGER)
    private Map<Product, Integer> products = new HashMap<Product, Integer>();

    // get/set
    // ...
}

@Embeddable
/* Only used in variation 1 */
public class ProductCount{
    @OneToOne
    private Product product;

    @Column
    private Integer amount;

    // get/set
}

@Entity
public class Product
{
    // ...
}

Then this is called and displayed using something like this (this is for variation 2)

<!-- Called via DAO/Service layers
List<Order> orders = getSession().createCriteria(UserOrder.class).list();
-->
<c:forEach items="${orders}" var="order">
    <fmt:formatDate value="${order.time}" type="both" />
    <c:forEach items="${order.products}" var="pc">
        ${pc.value} x ${pc.key.name}
    </c:forEach>
</c:forEach>

For the record, I am using Spring (3.1), Hibernate (3.5) and I’d like to stay with JPA annotations.

The Problem

When I retrieve the orders, I get a UserOrder-object for each of the products it contains, instead of one UserOrder for each order I have stored. So I get duplicates in my list, all with complete information of the products it contains. Orders without products are also included

• Order 1 — Has 2 products
  • 1 x DogToy1
  • 3 x Cat Toy 1
• Order 1 — Has 2 products
  • 1 x DogToy1
  • 3 x Cat Toy 1
• Order 2 — Has 1 product
  • 3 x Cat Toy 1
• Order 3 — Has 0 products

How do I make Hibernate return me one (1) UserOrder instead of one-for-each-product? Or, have I even taking the right approach to modelling this structure?

Answer 1

Options:

• lazy load the child collections (there should be an option to batch loading lazy loaded collections)
• use DistinctRootentityResulttransformer on the query