Yesterday I checked in a patch to the xml_content branch of the CVS that changes how Antville stores Stories and Comments in the relational DB. Instead of storing titles and bodies of stories in a separate column each, everything is encoded into an XML document using Helma's native XML extension and stored into a generic "content" column.

This great advantage to this is that it is now possible to add custom properties to stories (and, if desired, comments) with almost no effort. The only thing one has to do is to add macros for the custom parts both in the story (or comment) editor skin and in the story (or comment) skins where that part is to be displayed. Antville still requires a text property to be there, and text and title are assumed by some internal parts like the recently modified list. Other than that, there is no limit on the number and names of custom story properties.

The macro used to edit or display story properties is called content and it is very similar to the old title and text macros (which are still supported for backward compatibility), except that it requires an attribute called part describing the name of the content part to be edited or displayed. For example, editing a story title with the content macro looks like this:

<% this.content part="title" as="editor" width="24" style="formTitle" %>

while displaying a custom property called "teaser" might look like this:

<% this.content part="teaser" %>

The content macro takes one extra attribute called fallback, which describes a content part which is to be used in case that the one specified by the part attribute is not set. Thus, the following code

<% this.content part="teaser" fallback="text" %>

would display the content part called "teaser" if it exists and the content part called "text" if not. If a part is not defined, nothing is displayed.

I must say that I'm myself astounded by the flexibilty, simplicity and usefulness of this concept. A lot of things suddenly become very easy. Most of these are beyond what we will likely ever want to do with Antville, but it's still worth to pick out a few: stories in multiple languages, partitioning a story into multiple parts or over multiple pages, versioning ... the list goes on.

Here's a quick look into how this is implemented. All in all, it was surprisingly simple because of Stefan's XML Extension. I'm using the native dumping/reading of Hopobjects, so all I have to do is create a transient Hopobject and add the content parts to it as properties. The Hopobject can be transformed into an XML string in one call of XML.writeToString(hopobject), and converted back from XML to Hopobject calling XML.readFromString(xmlstring). Basically, story content is managed via these three simple functions in story/objectFunctions.js:

/**
 *  Get a content part by name.
 */
function getContentPart (name) {
   var cnt = this.getContent();
   return cnt[name];
}

/**
 *  Return the content parsed into a HopObject.
 */
function getContent () {
  if (!this.content)
     return new HopObject ();
  return Xml.readFromString (this.content);
}

/**
 *  Set the content of this story object.
 */
function setContent (cnt) {
    this.content = Xml.writeToString (cnt);
    var raw = "";
    for (var i in cnt)
       raw += cnt[i]+" ";
    this.rawcontent = raw;
}

(The last section in setContent() is used for writing the raw content without XML markup into a separate column for searching. I'm still thinking about other ways to search over story content. Just as a note, it would technically be possible to search for content in specific content parts using something like "%<partname>%searchterm%</partname>%".)

The XML that's written to the DB looks something like this:

<?xml version="1.0" encoding="UTF-8"?>
<!-- printed by helma object publisher     -->
<!-- created Wed Jun 12 18:52:09 CEST 2002 -->
<xmlroot xmlns:hop="http://www.helma.org/docs/gui
de/features/database">
  <hopobject id="t15" name="" prototype="hopobject" 
  created="1023900729721" 
  lastModified="1023900729722">
    <text>some text</text>
    <title>hello world!</title>
  </hopobject>
</xmlroot>

I hope this gave you a good impression of what this feature is about and how it works. I'm curious to hear what you think.

genius!

elegant and très très useful. that's how it is supposed to be ;-)

gefaellt!

i don't like the "fallback" parameter in the macro. how about using "default" instead?