Hi

I've come across this problem and I can't quite grasp the logic behind it. Appreciate it if anyone can help elaborate the why.

We have a simple parent-child relationship (self-referential table) with additional implementation of name sorting routine.
ID = PK
PARENT_ID = FK

And I have in the db:

ID | Name | PK
--------------------
CatA | CatA |
CatB | CatX | CatA
CatC | CatX | CatA


Understand that Set is "A collection that contains no duplicate elements". In theory, CatA will have 2 childrens (CatB, CatC). This is reflected correctly if I declare set in hbm.xml as
<set name="children" inverse="false">

However, after I implemented the comparator, CatA returns only 1 children (CatB).
<set name="children" inverse="false" sort="com.test.CatNameComparator">

I am guessing since Set does not allow duplicate elements, CatC is not being added as child because it share the same name as CatB. But the part I cant comprehense is why is it so when my PK is ID and not Name.



Below is the HBM and CatNameComparator.java.

----------------------------------------------------------------------------
<hibernate-mapping>
<class name="com.test.Cat" table="CAT">
<id name="id" column="ID" type="string" length="32">
<generator class="uuid.hex"/>
</id>

<property name="name" column="name" type="string" length="40"/>

<many-to-one name="parent" column="PARENT_ID" class="com.test.Cat" />

<set name="children" inverse="false" sort="com.test.CatNameComparator">
<key column="PARENT_ID"/>
<one-to-many class="com.test.Cat"/>
</set>

</class>
</hibernate-mapping>
----------------------------------------------------------------------------

public class CatNameComparator implements Comparator {

public int compare(Object o1, Object o2) {
String name1 = ((Cat)o1).getName();
String name2 = ((Cat)o2).getName();

return name1.compareTo(name2);
}
}

----------------------------------------------------------------------------

What does your equals and hashcode methods look like? It is your hashcode method that will determine a 'duplicate' in a HashSet not simply what you have defined as your PK.

This looks like a pure Java issue.

Acknowledged this is a java issue. I have double checked and still can't figure out what goes wrong.

I've tried setting hashCode() and equals() to getId() and getName() but results is always the same.

Anyone with sharp eye pls help points out my mistake.

Thx
-WK-

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public class Cat implements Serializable {

private String id;
private String name;
private Cat parent;
private SortedSet children;
private Date modified;


public Cat(String name) {
this.name = name;
this.modified = Calendar.getInstance(java.util.Locale.US).getTime();
}

public Cat() {
}

public String getId() { return this.id; }
public void setId(String id) { this.id = id; }

public String getName() { return this.name; }
public void setName(String name) { this.name = name; }

public void setModified(Date u) { this.modified = u; }
public Date getModified() { return this.modified; }

public Cat getParent() { return this.parent; }
public void setParent(Cat c) { this.parent = c; }

public SortedSet getChildren() { return this.children; }
public void setChildren(SortedSet c) { this.children = c; }


///////////////////////////////////////////////////////////////////
public void addChild(Cat child) {
if(children == null) children = new TreeSet();

child.setParent(this);
children.add(child);
}

public boolean equals(Object other) {
if ( !(other instanceof Cat) ) return false;

Cat castOther = (Cat) other;
return new EqualsBuilder()
.append(this.getId(), castOther.getId())
.isEquals();
}

public int hashCode() {
return new HashCodeBuilder()
.append(getId())
.toHashCode();
}
}

<class name="com.test.Cat" table="CAT">
<id name="id" column="ID" type="string" length="32">
<generator class="uuid.hex"/>
</id>

<version name="modified" column="MODIFIED" type="timestamp" unsaved-value="null" />

<property name="name" column="NAME" type="string" length="40"/>

<many-to-one name="parent" column="PARENT_ID" class="com.test.Cat" />

<set name="children" inverse="true" cascade="all" sort="com.test.CatNameComparator">
<key column="PARENT_ID"/>
<one-to-many class="com.test.Cat"/>
</set>

</class>

Have you had a chance to read this yet?

http://www.hibernate.org/109.html

I would recommend reading this 3 times and then once you think you understand it, read it again.

2 weeks after you get what you think is an implementation, read it again since what you did still probably doesn't work :)

If I seem cynical it is because we have been trying to define a eq/hc that will work for us in all scenarios with not a whole lot of success.

Other than that have you tried tracing your hashcode method to see when it is getting called and what the id is at that point?

I had a fun scenario earlier this week where I was using an ID from a parent many to one in a composite primary key and serializing my object. Upon deserialization the child object was being added into the parent's hashset before the id was available and chaos ensued.