proposal for new implementation of MMObjectNode.getRelated(String type)

[Marcel Maatkamp]

Hi,

We are seeing some serious performance-issues in the MMObjectNode.getRelated(type)
The way it works now is as follows:

 MMObjectNode.getRelated((String type) { 
     mmbase.get_*ALL*_related_nodes(this)
     while(moreElements()) { 
         if(node.otype = mmbase.getMMObject(type)) // compare the 2 otypes
             result.add(node);
     }
 }

This is fine if the node only has a few related nodes. But what happens with a node
with a smackload of relations but I only want to select, say, the related images..?
Needless to say, this method is highly inefficient.

Another issue arises when inheritance is used for the builders. Consider 2 types
of builders, Persons and Doctors (inher. persons). The current implementation
will fail to deliver the related Doctors when asked to return the Persons (different 
otypes).

Proposed sollution:

Rebuild the getRelated to use MultiRelations. Query looks like this:
 
    public Vector getRelatedNodes(String type) {
        Vector results = new Vector();

        Vector tables = new Vector();
        tables.addElement(this.parent.getTableName());
        tables.addElement(type);

        Vector fields = new Vector();
        fields.addElement(type + ".number");

        Vector directions = new Vector();
        directions.addElement("UP");

        String where = "";

        // retrieve related nodes of type 'type'
        Vector tussenresults = multirelations.searchMultiLevelVector(
            getNumber(),fields,"NO",tables,where,new Vector(),directions);

        // virtual node -> real node
        Enumeration e = tussenresults.elements();
        while(e.hasMoreElements())
            results.addElement( 
this.parent.getNode(((MMObjectNode)e.nextElement()).getStringValue(type+".number")) );

        return results;
    }

This query will return *only* the valid nodes, instead of all related, discarding the 
ones
with a wrong type. And it will fix the inheritance-problems since the tables are
now queried with their names, instead of the selection on otype.

I have implemented this in our system and it seems to run fine. If somebody with
MySql wants to test this, please mail me and I will give the source (or copy the
sample above into MMObjectNode). Rob?

Please discuss :)

gr,
 marcel