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From Clinton Begin <clinton.be...@gmail.com>
Subject Re: iBatis annotation related questions
Date Thu, 18 Feb 2010 15:58:04 GMT
Hi Jan,

>> expectations come from iBatis 3 Whitepaper

Just to be clear, it wasn't a "white paper" it was a community whiteboard
for brainstorming ideas. So it contained goals and ideas, but there was
never a commitment to any of them.


>> Multilevel Configuration

Ultimately I decided not to implement it this way because it became hard to
trace where behavior was configured.  To fully understand how a statement
might behave or perform, you would have had to look in 3 places.  I wasn't
satisfied with that, so I made it to be either XML or Annotations per
statement.  You can happily mix mappers with annotations or xml statements,
but each statement must use either one or the other.

>> to state all properties in order to alter the single one

That's configurable.  See the docs under the automappingBehavior setting (I
think that's what it's called).

>>annotations

You think it's unpleasant?  You should have seen me the day that I had to
remove WORKING CODE from my system because Sun changed the behavior of Java
Annotations between Java 1.5 and 1.6.

In a nutshell, circular references are not supported in the Annotations
framework.  All of your best hopes and dreams of having something better are
dashed by this one limitation.  There was a workaround in Java 1.5, but Sun
considered it a compiler bug, so they "fixed" the workaround in JDK 1.6.  If
you want to see it, you can dig back through a few hundred commits and see
where I removed that behavior.

A shame.  If this was C# I would have been able to fully realize the vision
of where we wanted to take the annotation (or attributes in C#) approach.

**>> 3 combinations of annotations and xml

In general, I recommend using annotations for simple things, and use XML for
anything more complicated.  Sorry, but Java annotations are just too messy,
limited and ugly.  There's a million reasons why we had to scale back the
behavior and limit it to what you see now.  If you want to understand why, I
encourage you to try to implement some of your suggestions.  You'll find the
same challenges.

>> 4 automatic (generated) SQL

Yes, I completely ditched the idea of generating SQL.  It's just a road that
I wasn't prepared to take iBATIS down.

>> 5 dynamic sql in annotations

Yes, SelectProvider and the SQL Builder framework are the only way (other
than writing your own).  I wasn't about to start putting XML embedded in SQL
embedded in strings embedded in annotations... that's out of hand and bad
practice IMHO.

I appreciate your questions, but please realize that everything was
considered.  Some things were left out for very good design reasons, others
because of limitations in Java and others we might just not have had a
chance to implement yet.

Clinton

2010/2/18 Ing. Jan Novotný <novotnaci@gmail.com>

> Hello,
>
>    I am going to have a presentation about iBatis 3 at Czech JUG. I have a
> 3-year experience with iBatis-2 and now I am doing little research on what's
> new in upcoming iBatis 3 release. Most of my expectations come from iBatis 3
> Whitepaper at the iBatis Confluence site. Now I am testing the new version
> and there are some things I didn't expect. I will be very pleased if anyone
> capable could answer me following questions so that I may forward them to
> the attendees of CZ JUG:
>
> *  1) multilevel configuration*
>       Firstly I thought that there would be a chance to override less
> prioritized level of configuration. Meaning, that if I have SQL represented
> in an @Select annotation and I create XML statement in mapper file with the
> same name, this XML declaration will take over the annotation and will be
> used instead. Reality is that iBatis will fail to start complaining about
> duplicate declaration. As I discovered, I can use only one or the other way
> - I can combine XML file with annotation based Java DAO, but they must not
> overlap in the sense of statement declaration. Is that right? Why is that
> done this way?
>       Next I thought there could be some means to explicitly say, that some
> parts of the lower configuration level fit for me and therefore ease my life
> a little. Let say I have ResultMap statement in XML configuration and 95% of
> its properties is fine by convention, but I need only to specify more single
> property or declare association / collection mapping. In that case I have to
> state all properties in order to alter the single one that is needed to be
> extra taken care of (or at least these are my findings from the tests I
> wrote). What I really want to say is: use convention to all properties
> except those that I explicitly configure in XML - that is not possible, is
> it?
>
> *  2) annotations*
>       Another unpleasant surprise was, that I am not able to get along with
> annotations to specify <collection> mapping - annotation @Collection is
> missing. Also @Association is not present - but as I discovered, it's
> possible to write @Result annotations in the way that associated object gets
> mapped. In documentation I found a statement, that annotations in Java
> aren't powerfull enough to make some things possible, but I can't make up
> why @Collection annotation is not possible to be made.
>
> *  3) combination of XML and annotations*
>       I tried combination of XML and annotations (due to lack of
> @Collection annotation) to specify @Select annotation but specify output as
> a ResultMap mapping in the XML configuration. But that's not possible too.
> Mixing configuration from annotations and XML is not possible in any way I
> guess. Ok, but is there any way how to reuse my annotations, to get the same
> behaviour as reusing ResultMap mapping in different statements of XML
> configuration?!
>
> *  4) automatic SQL implementation*
>       I didn't find any piece of this functionality. May I take it, that
> this was completely discarded?
>
> *  5) annotations and dynamic SQL*
>       Finally I didn't find any clue how to use dynamic SQL in annotations.
> Does that mean that @SelectProviders are the only way how to make dynamic
> queries by the Java code?
>
>    Thanks for your time and answers I can use in my presentation if anyone
> asks. Please, don't be offended by my questions, generally I think iBatis is
> a great DAO framework.
>
> Cheers Jan
>
> --
> --------------------------------------------------------------
> Ing. Jan Novotný
> @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
> http://blog.novoj.net
> Myšlenky dne otce Fura
> --------------------------------------------------------------
>

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