<?php

class TestTable extends DataObject
{
   static $db = array(
      'Name' => 'Text',
      'DateFrom' => 'Date',
      'DateTo' => 'Date',
   );

   public static $summary_fields = array (
      'Name' => 'Name',
   );

   function getCMSFields()
   {
      $fields = parent::getCMSFields();

      $fields->replaceField('Name',new TextField('Name'));

      $df1 = new DateField('DateFrom', 'DateFrom');
      $df1->setConfig('showcalendar', true);
      $fields->replaceField('DateFrom', $df1);

      $df2 = new DateField('DateTo', 'DateTo');
      $df2->setConfig('showcalendar', true);
      $fields->replaceField('DateTo', $df2);

      return $fields;
   }

   function getCMSValidator()
   {
         return new TestValidator();
   }
}

<?php

class TestValidator extends Validator
{

   function javascript()
   {
      return false;
   }
   function php($data)
   {
      $bRet = true;

      if (empty($data['DateTo']))
      {
         $this->validationError(
            'DateTo',
            'DateTo is required',
            "required"
         );

         $bRet = false;
      }

      if (empty($data['DateFrom']))
      {
         $this->validationError(
            'DateFrom',
            'DateFrom is required',
            "required"
         );

         $bRet = false;
      }

      return $bRet;
   }
}

<?php

class TestAdmin   extends ModelAdmin
{
   static $managed_models = array(
      'TestTable',
   );

   static $url_segment = 'testadmin';
   static $menu_title = 'Test Admin';

   static $model_importers = array();

}