Hello.
From the TreeDropdownField API, it's my understanding that the $keyField is the column in the $sourceObject where the data that will be stored will come from. If I do the following:

class HomePage extends Page
{
   function getCMSFields()
   {
      $fields = parent::getCMSFields();
            $fields->addFieldToTab('Root.Content.Buttons', new TreeDropdownField('LinkID', 'Choose a page to Link to:', 'SiteTree', 'URLSegment'));
      return $fields;
   }
}

I would expect that in my table (HomePage), the "LinkID" column will be a varchar that stores the URLSegment. However, when I do a dev/build, the follwoing is created:
Field HomePage.LinkID: created as int(11) not null default '0'

It appears that the build ignores the $keyValue and sticks with the default of "ID". While the form functionality is as expected, when I save, I only get the default 0 in the row (as I would expect based on how the table was created).

I feel like I may be missing a something, I've tried something like this:

class HomePage extends Page
{
   static $db = array(
       'LinkID' => 'Text'
   );
.
.
.

but that just gets ignored.

Any ideas as to what I'm doing wrong?

Cheers.

After reading through the TreeDropdownField.php code, I did a small experiment and dropped the HomePage(_Live, _versions) tables after the build and recreated them with the URLSegment data type:

CREATE TABLE `HomePage` (
  `ID` int(11) NOT NULL auto_increment,
  `LinkID` varchar(255) character set utf8 default NULL,
  PRIMARY KEY  (`ID`),
  KEY `LinkID` (`LinkID`),
) ENGINE=MyISAM AUTO_INCREMENT=2 DEFAULT CHARSET=latin1;

That did the trick and everything worked as expected... of course if I rebuild the db (/dev/build), it flips it back:

Field HomePage.LinkID: changed to int(11) not null default '0' (from varchar(255) character set utf8 collate utf8_general_ci)

And it's broken again. So it looks like TreeDropdownField is doing what its supposed to per the API, but the build is not creating the table right.

Is this a bug in the build? or am I missing something that will tell the build to create column with the URLSegment datatype?

In case anyone is trying to do the same thing... I figured it out by starting from scratch:

   static $db = array(
       'LeftURL' => 'VARCHAR(255)',
   );
   static $has_one = array(
   );
   function getCMSFields() 
   {
      $fields = parent::getCMSFields();
      $fields->addFieldToTab('Root.Content.Buttons', new TreeDropdownField('LeftURL', 'Choose a Left Image Link:', 'SiteTree', 'URLSegment'));
      return $fields;
   }