Tree Structure - Not working, why?

marioti · **Joined:** Thu Feb 09, 2006 10:50 pm **Posts:** 7

I'm trying to make a tree structure using HB, But a got a weird problem I don't know how to solve:

I insert some nodes to the tree, everything go ok.

When I try to get them back(createCriteria and/or createQuery), the getChildren List is ALWAYS null. getParent works fine.

Can you guys help me? Thank you a lot.

All files:

Hibernate version:305

Mapping:

Code:

<hibernate-mapping>
    <class name="br.com.meta.satie.hb.sistema.Node" lazy="true">
        <id name="id">
            <generator class="increment"/>
        </id>

        <property name="title"/>
        <property name="path"/>
        <property name="iconPath"/>
        <property name="sequence"/>
        
       <list name="children" table="node" 
            cascade="all-delete-orphan" inverse="true" lazy="true">
          <key column="idParent" />
          <index column="sequence" />
          <one-to-many class="br.com.meta.satie.hb.sistema.Node" />
      </list>

        <many-to-one
        name="parent"
        class="br.com.meta.satie.hb.sistema.Node"
        column="idParent"
        cascade="all"/> 

    </class>
</hibernate-mapping>

INSERT

Code:

        Transaction tx = session.beginTransaction();
        
        Node ROOT = new Node();
        ROOT.setTitle("ROOT");
        ROOT.setParent(null);
        ROOT.setSequence(0);
        ROOT.setPath("ROOT path");
        
        Node CHILD1 = new Node();
        CHILD1.setTitle("CHILD1");
        CHILD1.setParent(ROOT);
        CHILD1.setSequence(0);
        CHILD1.setPath("CHILD1 path");
        
        Node CHILD2 = new Node();
        CHILD2.setTitle("CHILD2");
        CHILD2.setParent(ROOT);
        CHILD2.setSequence(0);
        CHILD2.setPath("CHILD2 path");
                
        
        session.save(ROOT);
        session.save(CHILD1);
        session.save(CHILD2);
        
        tx.commit();

QUERY:

Code:

        Query select = session.createQuery("from Node n left join fetch n.children");
        List<Node> nodes = select.list();
        for(Node n: nodes) {
            System.out.println("NODE: " + n.getId() + " PARENT: " + n.getParent() + " CHILDREN: " + n.getChildren());
          
        }  

Name and version of the database you are using:
MySQL

The generated SQL (show_sql=true):

Code:

Hibernate: /* insert br.com.meta.satie.hb.sistema.Node */ insert into Node (title, path, iconPath, sequence, idParent, id) values (?, ?, ?, ?, ?, ?)
Hibernate: /* insert br.com.meta.satie.hb.sistema.Node */ insert into Node (title, path, iconPath, sequence, idParent, id) values (?, ?, ?, ?, ?, ?)
Hibernate: /* insert br.com.meta.satie.hb.sistema.Node */ insert into Node (title, path, iconPath, sequence, idParent, id) values (?, ?, ?, ?, ?, ?)
Hibernate: /* from Node p left join fetch p.children c */ select node0_.id as id0_, children1_.id as id1_, node0_.title as title0_0_, node0_.path as path0_0_, node0_.iconPath as iconPath0_0_, node0_.sequence as sequence0_0_, node0_.idParent as idParent0_0_, children1_.title as title0_1_, children1_.path as path0_1_, children1_.iconPath as iconPath0_1_, children1_.sequence as sequence0_1_, children1_.idParent as idParent0_1_, children1_.idParent as idParent0__, children1_.id as id0__, children1_.sequence as sequence0__ from Node node0_ left outer join Node children1_ on node0_.id=children1_.idParent

SYSTEM OUTPUT:
NODE: 1 PARENT: br.com.meta.satie.hb.sistema.Node@8e32e7 CHILDREN: null
NODE: 2 PARENT: null CHILDREN: null
NODE: 2 PARENT: null CHILDREN: null
NODE: 3 PARENT: br.com.meta.satie.hb.sistema.Node@8e32e7 CHILDREN: null
BUILD SUCCESSFUL (total time: 5 seconds)

spatik · **Posted:** Thu Feb 09, 2006 11:20 pm

Did you have any sequence values for the object you are trying to retrieve by List?

If you don't have it might return null?

:-)

marioti · **Joined:** Thu Feb 09, 2006 10:50 pm **Posts:** 7

I tried to set some diferent values on sequence field: (1, 2) for child nodes and (0, 1) for root node... got the same result. :(

spatik · **Posted:** Thu Feb 09, 2006 11:34 pm

I dunno if this will work. But try to add this to your list and <many-to-one> mapping ------ fetch="join".

Reply if it helped and even if hadn't :-)

marioti · **Joined:** Thu Feb 09, 2006 10:50 pm **Posts:** 7

Same problem...

Look, I found an example but it does not works too (getChilds)

http://www.satollo.com/en/programming/h ... -tree.html

spatik · **Posted:** Thu Feb 09, 2006 11:45 pm

Just do a quick check if,
hibernate.max_fetch_depth is set to 0 in your hibernate file.

marioti · **Joined:** Thu Feb 09, 2006 10:50 pm **Posts:** 7

yep:

<property name="hibernate.max_fetch_depth">0</property>

spatik · **Posted:** Thu Feb 09, 2006 11:52 pm

If it is 0, it might not allow joins to fetch data.
That's what the hibernate manual says.

Quote:

Outer join fetching may be disabled globally by setting the property hibernate.max_fetch_depth to 0. A setting
of 1 or higher enables outer join fetching for one-to-one and many-to-one associations which have been
mapped with fetch="join".

Try removing it.

marioti · **Joined:** Thu Feb 09, 2006 10:50 pm **Posts:** 7

It was not set before, I just inserted it now (and removed), both ways give me the same result (getChildren == null)

A lot of people had the same problem (google it) I'm starting to think it's a hibernate problem.

marioti · **Joined:** Thu Feb 09, 2006 10:50 pm **Posts:** 7

Yes, I almost sure this is a hibernate bug (some bidirectional problem)

On the first insert-code, I tried to use session.flush but I got some problem, now I tried to addChildren instead of setting parent and it is working. This is VERY crazy, because the data on the mysql table is the same in both ways.

Code:

      Transaction tx = session.beginTransaction();
        
        Node ROOT = new Node();
        ROOT.setTitle("ROOT");
        ROOT.setParent(null);
        ROOT.setSequence(3);
        ROOT.setPath("ROOT path");
            
        ArrayList l = new ArrayList();
        Node CHILD1 = new Node();
        CHILD1.setTitle("CHILD1");
        CHILD1.setSequence(1);
        CHILD1.setPath("CHILD1 path");
        l.add(CHILD1);
        
        
        Node CHILD2 = new Node();
        CHILD2.setTitle("CHILD2");
        CHILD2.setSequence(2);
        CHILD2.setPath("CHILD2 path");
        l.add(CHILD1);
                
        ROOT.setChildren(l);
        
        session.save(ROOT);
        session.save(CHILD1);
        session.save(CHILD2);
        
        tx.commit();    

spatik · **Posted:** Fri Feb 10, 2006 12:13 am

Did you check your databse if the values has been set correctly?

I tried to reproduce your issue and the only problem i face is that when i retrieve a list and order it by the index sequence, it inserts null values in the list.

Like,
Say i have three children with sequence values 3, 4 and 7.
Now on retrieving the list i get 7 values in the list with first and second being null and the third being the child with sequence value 3, 4th being the child with sequence value 4 adn 5 and 6 are again null with 7th child being the child with sequence value 7.

But i do get a children list collection with all the 7 values.

spatik · **Posted:** Fri Feb 10, 2006 12:20 am

Hah!!! Now is see your problem.
You specify that this child node has the parent_id as the parent node's id.

But the parent node's id is generated only after the parent node is actually inserted into the database. so it should first insert the parent node, get the id of it and use it to set the ParentId of the child node.

So it should be cascaded. But if you save your three nodes as,

session.save(Parent node);
session.save(Child node1); // it doesn't know the parent node's ID.
session.save(Child node2); // it doesn't know the parent node's ID.

On your second approach,
You don't have to give,

session.save(Child node1);
session.save(Child node2);

It's enough if you just say session.save(parent node);
Try now it'll work for you.

It's not a hibernate problem. :-)

Please vote if my postings helped you.

marioti · **Joined:** Thu Feb 09, 2006 10:50 pm **Posts:** 7

Thank you a lot, now I think I know what is the problem,

I don't know why, but even using session.flush() HB it's not returning child nodes if I'm using just child.setParent(root) to save them. And, if I'm using just root.addChildren(arraylist) without setParent on every child, it doesn't works too.

IMHO:
The HB reference says session.flush avoid this (you don't need to set on both sides of the relationship) but somehow it's doesn't works when the relationship it's on the same table. (Using 2 diferent tables, this works)

This "solved" my problem (I'm making some tests):

Code:

    public void addChild(Node child) {
        if (children == null) children = new ArrayList<Node>();
        child.setParent(this);
        children.add(child);
    }