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From Vadim Gritsenko <va...@reverycodes.com>
Subject Query and QueryByCriteria
Date Thu, 24 Mar 2005 18:31:24 GMT
Hi All,

I would like to introduce new Query implementation, which is a simplified 
version of the QueryByCriteria - it does not support arbitrary criterias but 
only criterias with certain structure [1].

While working on impementation, I noticed, that despite the fact that there is 
base interface - Query - OJB relies in many parts on particular class - 
QueryByCriteria. So for my query implementation I have several ways of working 
this around:

   * Extend my query class from QueryByCriteria and override some methods
     to disable extra functionality. OJB internals will remain unchanged,
     mostly, and will still rely on QueryByCriteria.

   * Introduce base abstract class which replaces QueryByCriteria. OJB
     internals can rely on this abstract class instead of concrete
     QueryByCriteria class with lots of implementation details.

   * Extend Query interface to incorporate methods introduced in
     QueryByCriteria. OJB internals can rely on interface instead
     of concrete class.

   * Any other good approach which I missed?

Now question, which way is the most appealing way to OJB developers? My goal is 
to have these changes incorporated back into OJB, so I'd like to take the 
approach which is preferred by OJB team.


Another question I had is of more abstract nature... Why OJB's Query 
implementations are not immutable objects? It does prevent caching of Query 
obhects, multithreaded usage of Query objects, etc. To me, ideal OJB 
architecture would rely on Query interface and treat Query instances as 
immutable objects - so that new Query implementations can be plugged in easily, 
and Query objects themselves can be passed on by reference without any problems.


[1] This new Query will implement query-by-primary-ley and query-by-reference 
functionality - with support of plain SQL as well as stored procedures. As a 
side effect, it will provide some query-by-example-object functionality. Current 
QueryFactory.newQuery(Object example) is confusing to me - it can not really 
create a query by example object, only query by primary key, right?

Thanks,
Vadim


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