Can't fetch two lazy collections!?
I was rather surprised to see this exception:
Caused by: org.hibernate.HibernateException: cannot simultaneously fetch multiple bags at org.hibernate.loader.BasicLoader.postInstantiate(BasicLoader.java:66) at org.hibernate.loader.hql.QueryLoader.<init>(QueryLoader.java:100) at org.hibernate.hql.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:180) at org.hibernate.hql.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:110) at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:77) at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:56) at org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:71) at org.hibernate.impl.AbstractSessionImpl.getHQLQueryPlan(AbstractSessionImpl.java:133) at org.hibernate.impl.AbstractSessionImpl.createQuery(AbstractSessionImpl.java:112) at org.hibernate.impl.SessionImpl.createQuery(SessionImpl.java:1612) at org.hibernate.ejb.AbstractEntityManagerImpl.createQuery(AbstractEntityManagerImpl.java:76) ... 70 more
I have an entity called Order which has two lazy collections:
@Entity
@Table(name="tbl_order")
public class Order implements Serializable
{
private List<Address> addresses;
private List<OrderLine> orderItems;
private List<TrackingNumber> trackingNumbers;
public Order()
{
}
@OneToMany(mappedBy="order", fetch=FetchType.LAZY, cascade=CascadeType.ALL)
public List<Address> getAddresses()
{
return this.addresses;
}
public void setAddresses(List<Address> addresses)
{
this.addresses = addresses;
}
@OneToMany(mappedBy="order", fetch=FetchType.LAZY, cascade=CascadeType.ALL)
public List<OrderLine> getOrderItems()
{
return this.orderItems;
}
public void setOrderItems(List<OrderLine> orderItems)
{
this.orderItems = orderItems;
}
@OneToMany(mappedBy="order", fetch=FetchType.LAZY, cascade=CascadeType.ALL)
public List<TrackingNumber> getTrackingNumbers()
{
return this.trackingNumbers;
}
public void setTrackingNumbers(List<TrackingNumber> trackingNumbers)
{
this.trackingNumbers = trackingNumbers;
}
}
The EJB-QL that caused the problem is:
..........
String query = "select o from Order o " +
"left join fetch o.addresses a " +
"left join fetch o.orderItems ol " +
"where o.id = :orderId";
Query q = this.em.createQuery(query);
q.setParameter("orderId", orderId);
..........
Why can't I "left join fetch" preload more than one of these collections at the same time? I was originally eagerly-loading the addresses but I decided that this was bad due to how my application uses this data...it would deteriorate performance at a level I'm not happy with.
Is this a bug or a limitation?
Thanks!
