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From: "C N Davies" <cnd@cndavies.com>
To: "'Daryl Stultz'" <daryl@6degrees.com>,
	<users@openjpa.apache.org>
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Subject: RE: Dynamic entity definition creation - is it possible?
Date: Fri, 24 Jul 2009 01:59:57 +1000
Organization: C N Davies Pty Ltd
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Hi Daryl,

 
Thanks for your thoughts, your idea is interesting food for thought indeed.

 
I'm a bit of a puritan when it come to abstractions, and while abstraction
is a great thing I must confess to feeling that sometime I take it to the
n'th degree and try push it too far.  

 
Lately I have been developing my first JPA application and after much
research and soul-searching I went with OpenJPA rather than using Hibernate
experience (non-JPA version) despite the fact that it's blowing out my
timeframes, because I always find Apache software to be innovative and high
quality.

 
All of my entities are created (integrated using a fileinputstream of CSV or
XLS/XLSX) using a model whereby I read the file headers then search for a
setter method that  uses "set"<column header name>, then call the setter.

 
My next step is to load data columns that won't have setter methods on the
entity class because at build time I may not know the additional custom
field names.  I guess my challenge is that since I know the entity won't
have setters for the new column names in the data set,  I want to be able to
modify the entity calss at runtime to add the required setter method, then
let the enhancer process the newly modified entity definition, then call the
new setter method to let OpenJPA handle things as if I had defined these new
entity members at design time.

 
I could do this using JPA queries but it seems a little adhoc or impure, so
I'm trying to think of a way of doing this without busting my puritanical
vision.

 
Chris

 
From: Daryl Stultz [mailto:daryl@6degrees.com] 
Sent: Friday, 24 July 2009 1:18 AM
To: users@openjpa.apache.org; cnd@cndavies.com
Subject: Re: Dynamic entity definition creation - is it possible?

 
On Thu, Jul 23, 2009 at 11:02 AM, C N Davies <cnd@cndavies.com> wrote:

I might be thinking in the wrong direction so feel free to berate me if I
am.

 
I'd like to berate you for building a self-modifying system, but I've done
it myself, so I won't. I do have a project (not the self-modifying one) that
has a need for adding "custom properties" to an entity. The entity has its
core properties in the main table, then a list of custom properties in
another table. Custom properties have a "definition" that describes
datatype, presentation order and whatnot. In my pre-JPA system, presenting
such an entity would involve a "pivot" on the custom properties. This is
also required for JPA but you get it for "free" in that the custom property
values come into the collection and it's easy enough to work with it in the
rendering layer.

 
I'm looking for ways to improve my solution, so don't think I'm proposing it
as an alternative to yours. I am interested in how my solution would not
work for you.

 
-- 
Daryl Stultz
_____________________________________
6 Degrees Software and Consulting, Inc.
http://www.6degrees.com
mailto:daryl@6degrees.com


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