1-to-many and collections question

Question

I'm modeling a standard container and container elements relationship using
Kodo.
I'm also trying to be fairly RDBMS efficient, so I'm using the kodo inverse
properties
avoid the extra 'mapping' table.
Here is a simplification:
class Container
private Collection myChildren = new ArrayList();
// + more properties
public Collection getChildren() { return myChildren;}
class ContainerElement
// only have this so Kodo can use reverse property mappings
private Container myParent = null;
// + more properties
public void setParent(Container c) { myParent = c;}
// here is the code snippet from the Container.jdo
<field name="myChildren">
<collection element-type="ContainerElement"/>
<extension vendor-name="kodo" key="inverse"
value="myParent"/>
</field>
Now what I would like to do is this:
Container c = new Container();
c.getChildren().add(new ContainerElement())
c.getChildren().add(new ContainerElement())
and have the parent property automatically set.
Basically the question is:
How can I do Containers through the Coolection APIs, and have the underlying
RDBMS use standard 1-Many by having a parent column?
Thanks for looking into this.
--Eivind Skildheim
Motive Communications, Inc

Answer 1

Eivind-
Could I implement my own collection by subclassing AbstractList (or
AbstractSet) that upon add calls the setParent method?The persistent member itself can only be an instance of that custom
List/Set implementation if you implement your own ProxyManager so
Kodo knows how to maintain the proxies for those classes. Take a look
at:
http://www.solarmetric.com/docs/2.4.0/docs/manual.html#com.solarmetric.kodo.ProxyManagerClass
A simpler solution might be to have the class implement
InstanceCallbacks, and then implement jdoPreStore() to ensure that your
relations are set up correctly. E.g.,
public void jdoPreStore ()
// ensure that all the elements of the children collection
// have the proper parent set in the inverse of the relation.
for (Iterator i = myChildren.iterator (); i.hasNext ();
((Child)i.next ()).setParent (this));
Another option is to have your accessor methods just wrap the collection
in a small decorator that does the right thing when elements are added.
In article <[email protected]>, Eivind Skildheim wrote:
Thanks for the answer.
Could I implement my own collection by subclassing AbstractList (or
AbstractSet)
that upon add calls the setParent method? The collection would take the
inverse
property name as a constructor argument and lookup up the property by
reflection.
The questions is: Is that safe in regards to bytecode enhancement.
Thanks,
Eivind Skildheim
"Marc Prud'hommeaux" <[email protected]> wrote in message
news:[email protected]...
Eivind-
It is a common question that people have why their JDO model does not
automatically retain inverse relations in the java model. This is
because that JDO's transparency means that your enhanced classes should
not behave any differently than normal java classes. Thus, it is the
responsibility of the application programmer to ensure that their data
model remains consistent, just as they would have to in a normal,
non-JDO application.
In your case, you could just have a method that deals properly with the
relation. E.g.:
public class Parent
private Collection children = new HashSet ();
public void addToChildren (Child child)
children.add (child);
child.setParent (this).
In article <[email protected]>, Eivind Skildheim wrote:
I'm modeling a standard container and container elements relationship
using
Kodo.
I'm also trying to be fairly RDBMS efficient, so I'm using the kodoinverse
properties
avoid the extra 'mapping' table.
Here is a simplification:
class Container
private Collection myChildren = new ArrayList();
// + more properties
public Collection getChildren() { return myChildren;}
class ContainerElement
// only have this so Kodo can use reverse property mappings
private Container myParent = null;
// + more properties
public void setParent(Container c) { myParent = c;}
// here is the code snippet from the Container.jdo
<field name="myChildren">
<collection element-type="ContainerElement"/>
<extension vendor-name="kodo" key="inverse"
value="myParent"/>
</field>
Now what I would like to do is this:
Container c = new Container();
c.getChildren().add(new ContainerElement())
c.getChildren().add(new ContainerElement())
and have the parent property automatically set.
Basically the question is:
How can I do Containers through the Coolection APIs, and have theunderlying
RDBMS use standard 1-Many by having a parent column?
Thanks for looking into this.
--Eivind Skildheim
Motive Communications, Inc
Marc Prud'hommeaux [email protected]
SolarMetric Inc. http://www.solarmetric.com
Marc Prud'hommeaux [email protected]
SolarMetric Inc. http://www.solarmetric.com