Re: [Hibernate-devel] XML databinding.

[Gavin_King/Cirrus%<CI...@ci...>]

> Why was JDom chosen as the XML toolkit of choice?  I
> think using Dom4J or something else that supports
> XPath would make life much easier in the mapping file.

Actually to parse mapping files (DOCTYPE hibernate-mapping.dtd)
I'm using vanilla JAXP. This was probably a mistake. JDOM
is used to construct XML representation of persistent objects.
Don't think XPATH would help us here. I've never used DOM4J.
Is it better than JDOM in other ways?

If I was redoing this from scratch I would take a close look
at using JAXB or something similar for parsing the mapping
file.

> I am currently working on an XML mapping system where
> I work (specific use) and am wondering what your plans
> are for XML.  Is it going to be the same interface as
> your SQL databinding?

I'm not sure if you realise, but XML generation is already
implemented. It just isn't documented in the tutorial. Check
the JavaDocs for a quick summary.

Start out with SessionFactory.openDatabinder()

Basically, when I got round to implementing this, I
had a look around and discovered that the open source
solutions for databinding had improved a whole lot
and I didn't want to try and waste time doing what
other people are doing better. I figured plenty
of other projects are trying to let you arbitrarily
map XML to objects and vice-versa. So I decided
to do something real simple.

1. I didn't want to introduce yet another OO to XML
mapping language.
2. I wanted XML generation for persistent classes to
"just work". ie. you don't need to do any mapping
at all most of the time.
3. I wanted it to be _possible_ to customize the
generated XML either on a per-class or whole
application basis.

My solution was to use XSLT as the mapping language
and provide a default stylesheet that does what you
would probably want. You can customize the stylesheet
to alter the mapping for individual classes, or for
all classes at once. I kinda like this.

So XML generation became a two-step process.

1. generate a "generic" XML representation that is
amenable to manipulation by XSLT and includes as
much information as you could possibly want.

  <object class="Foo" package="cirrus.hibernate.test">
    <uid name="key" type
="string">52b16c9d:ecc0e74d:00ec:c0e7d476:0011</uid>
    <property name="foo" type="cirrus.hibernate.test.Foo" />
    .....
  </object>

2. use Xalan to process that XML with the (custom
or default) stylesheet.

  <Foo id="N400005">
    <key>52b16c9d:ecc0e74d:00ec:c0e7d476:0011</key>
    <foo/>
    ......
  </Foo>


There would be some extra problems in going backward
from XML to Java but I didn't want to waste too much
time on that problem if no-one was using hibernate for
XML generation. (I guess I should start by documenting
it, though.)