Right.. well, tables are for flat data models. You're trying to flatten a model that is no longer flat. If your model had only one file attachment, you could use a table column for that field, but since you're now saying you have any number of file attachments, you can't have a uniform table anymore. The column count would be different on each row!

What you're describing doesn't make any sense. You're asking that each row of the table have a different number of columns.

Unless I'm misunderstanding you?

So you only have 3 attachments per object? Never more than that?

So just do this:

<?php
class Resource extends DataObject
{
static $db = array (
'Name' => 'Text',
'Description' => 'Text',
'Category' => "Enum('Industry, Finance, Education')",
);

static $has_one = array (
'File1' => 'File',
'File2' => 'File',
'File3' => 'File',
'ResourcePage' => 'ResourcePage'
);

public function getCMSFields_forPopup()
{
return new FieldSet(
new TextField('Name'),
new TextareaField('Description'),
new DropdownField('Category','Category', singleton('Resource')->dbObject('Category')->enumValues()),
new FileUploadField('File1'),
new FileUploadField('File2'),
new FileUploadField('File3')

);
}
}
?>

==================================

and this is the ResourcePage.php

<?php
class ResourcePage extends Page
{
static $has_many = array (
'Resources' => 'Resource'
);

public function getCMSFields()
{
$f = parent::getCMSFields();
$manager = new DataObjectManager(
$this, // Controller
'Resources', // Source name
'Resource', // Source class
array(
'Name' => 'Name',
'Description' => 'Description',
'Category' => 'Category',
'File1.Name' => 'File1',
'File2.Name' => 'File2',
'File3.Name' => 'File3',
), // Headings
'getCMSFields_forPopup' // Detail fields (function name or FieldSet object)
);

$f->addFieldToTab("Root.Content.Resources", $manager);

return $f;
}

}

class ResourcePage_Controller extends Page_Controller
{
}