First, let me say that Hibernate is awesome. I'm just now playing around with it, but really like! I'm seeing one weird behavior though:

Discription: The 'contains' method is returning false, but I know the given object is (the only object) in the set because:

a)It's iterator finds it:

assertEquals(hibernateSet.iterator().next(), givenObject);
//passes

b)Wrapping the hibernate Set in a java.util.HashSet results in 'contains' returning true:

jdkSet = new HashSet(hibernateSet);
assertTrue(jdkSet.contains(givenObject);

Hibernate Version: 2.1.4
Database Version: MySQL, 4.0.20a
mapping documents:

<hibernate-mapping>
<class name="tomcattest.PetOwner" table="pet_owner">
<id name="id" type="string" unsaved-value="null" >
<column name="id" sql-type="char(32)" not-null="true"/>
<generator class="uuid.hex"/>
</id>
<property name="name" column="name" type="string"
length="15" not-null="false"/>
<set name="pets" cascade="all" inverse="true" lazy="true">
<key column="pet_owner_id"/>
<one-to-many class="tomcattest.Pet"/>
</set>
</class>
</hibernate-mapping>

<hibernate-mapping>
<class name="tomcattest.Pet" table="pet">

<id name="id" type="string" unsaved-value="null" >
<column name="id" sql-type="char(32)" not-null="false"/>
<generator class="uuid.hex"/>
</id>

<property name="name">
<column name="NAME" length="16" not-null="true"/>
</property>
<property name="sex"/>
<property name="weight"/>
<many-to-one name="owner" class="tomcattest.PetOwner"
column="pet_owner_id"/>

<joined-subclass name="tomcattest.Cat" table="cat">
<key column="id"/>
<property name="outdoorCat" column="is_outdoor"/>
</joined-subclass>
<joined-subclass name="tomcattest.Dog" table="dog">
<key column="id"/>
<property name="huntingDog" column="is_huntingdog"/>
</joined-subclass>

</class>
</hibernate-mapping>

Java Code:
Failing Test:
...
Session session = HibernateUtil.currentSession(testConn);
Transaction tx= session.beginTransaction();

//write some data
PetOwner jenn = new PetOwner();
jenn.setName("Jenn");

Cat mama = new Cat();
mama.setName("Mama Kitty");
mama.setSex('F');
mama.setWeight(8);
mama.setOwner(jenn);
mama.setOutdoorCat(true)
session.saveOrUpdate(jenn);

//retrieve the data
List petOwners = session.find("From PetOwner");
assertEquals(1,petOwners.size());
assertTrue(petOwners.contains(jenn));

Set allPets = ((PetOwner)petOwners.get(0)).getPets();
System.out.println("Broken Set: " + allPets.getClass().getName());
//Above line outputs: net.sf.hibernate.collection.Set
assertEquals(allPets.size(),1);
assertEquals(allPets.iterator().next(), mama);
//Above assertion passes
assertTrue(allPets.contains(mama));
//Above assertion fails, BUG?

tx.rollback();
HibernateUtil.closeSession();
...

Thanks,
Mike

Most definitely a problem with your equals()/hashCode() implementation for the entities contained in the set.

Keep in mind that Hibernate strictly follows the java Set contract which says, in part, that the value of the elements equals() and hashCode() methods should not change while the object is an element within the Set. If it does change you end up seeing exactly the type of behaviour you are seeing.

Most likely you are basing equals() and hashCode() value on the db identity (i.e., the property mapped with the <id/> element). This is a problem if the entities contained in the set are created as part of a cascade because of there inclusion in a set.

Yep, my equals() was including the id attribute [I had only partially implemented hashCode(), since this was just a sample...]. I guess there's a lot of truth to the claim on this website "make sure you really understand hibernate...most of the things that seem like bugs with be due to your own code"! Thanks again...