Hashmap with Entity as Keys

alanhay · **Joined:** Tue Jul 29, 2008 7:01 am **Posts:** 9

There are a number of posts in the forum regarding problems when using Entities as Map keys, none of which have had any responses.

See here for an explanation of the issue:

http://forum.hibernate.org/viewtopic.ph ... entity+key

Is this a known limitation? Is there a workaround?

I am using Hibernate 3.3 but this seems to be a long standing issue.

Thanks.

Alan

cbredesen · **Posted:** Mon Feb 16, 2009 11:42 pm

It sounds like the linked post explains the issue. Have you tried making the Map not lazy? I would not expect a HashMap to work well on uninitialized proxies.

alanhay · **Joined:** Tue Jul 29, 2008 7:01 am **Posts:** 9

Tried a few things without success.

Code:

public class Course
{   
   @OneToMany(cascade=CascadeType.ALL)
   @JoinColumn(name="course_id", nullable=false)
   @ForeignKey(name="course_tees_courses_fk")
   @MapKey(name="teeType")
   private Map<TeeType, CourseTee> courseTees; 
}

Code:

public class CourseTee
{
   @ManyToOne(cascade=CascadeType.ALL, fetch=FetchType.EAGER)
   //@LazyToOne(value=LazyToOneOption.FALSE)
   @JoinColumn(name="tee_type", nullable=false)
   @ForeignKey(name="course_tees_tee_types_fk")
   private TeeType teeType;
}

TeeType equals and hashcode implemented correctly however map.contains(TeeType.X) always returns false.

Any ideas? Ditch the Map?

nordborg · **Posted:** Tue Feb 17, 2009 4:05 pm

Quote:

TeeType equals and hashcode implemented correctly however map.contains(TeeType.X) always returns false.

Sounds like there might be some problem with the implementation. We are using map:s with entities as keys without any problem. We have based the hashCode() and equals() on the ID only and we never (I hope) mix transient and persistent items in the same map.

It shouldn't be a problem to have proxies as keys in a map, since if the hashCode() or equals() method is implemented by the entity class the proxy will be initialized when any of those methods are called.

alanhay · **Joined:** Tue Jul 29, 2008 7:01 am **Posts:** 9

Unit testing would suggest Equals and Hashcode implementations are valid and that there are no issues getting values out of the Map for non-Hibernate managed objects.

When I run the test using an entity retrieved form the database via Hibernate, then:

TeeType nonHibernate = a;
TeeType fromHibernate = b;

[1] a.equals(b) is true
[2] a.hasCode() == b.hashCode() is true
[3] map.containsKey(a) = false;

equals() and hashcode() are not using the ID but some other field.