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From "Richard Sullivan" <itexpert.sulli...@gmail.com>
Subject Re: Proposed Enhancement - Support Multiple Parameter Classes
Date Tue, 10 Oct 2006 18:57:17 GMT
Jeff you took the words outta my mouth.  Your idea gets a humble +1 from me.

I've no idea about IBATIS internals but I think Jeff is proposing something
which would greatly increase the usability of the mapping.

I' m working on a team project where the persistence layer is my baby and I
hate exposing details of the persistence layer to the business layers.

For those who might see the problem I will briefly describe the shenanigens
I have used to workaround it.

For DB-trash think PK values and some information that I need in order to be
able how to sort out the mess when I read it back (for example a vector
position index value when reading back a vector of domain objects so that
the order is preserved).

I ended up writing PersistentX, PersistentY etc. where X and Y are the
domain objects and the PersistentX looks like this:

public class PersistenX extends {
    DBTrashValueClass dbTrash;

    // loads of getters/setters() each delegating to dbTrash
    long getPKCol1() { return dbTrash.getPKCol1(); }
    long getPKCol2() { return dbTrash.getPKCol2(); }
    int getOrderPosition() { return dbTrash.getOrderPosition(); }

Before the persistence layer  writes a domain object I have to  instantiate
a new "Persistent" object corresponding to the particular domain object,
copy all attributes of the domain object to the "Persistent" version (I do
this using Commons PropertyUtils), next I copy in all the DB persistence
control information (). After all this I can pass the PersistentX as a
parameter class for my INSERT.

This is a LOT of mucking around and is not a great example of object
oriented programming.

I did consider using aspects to somehow introduce the db-trash into the
domain objects rather than misusing inheritance for this task.  For my
present project this is a no-no (project manager wants a SIMPLE solution)
but if the IBATIS framework did the aspect magic then I probably would have
jumped at it.  I think Hibernate does something similar using byte-code
manipulation in some circumstances but I digress.  I'm not a great fan of
such tricks but they could be made optional.

Another enhancement that would probably make a huge difference would to be
able to use OGNL expressions to access nested properties of the parameter
class since often domain objects are nested.


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