Word Press Saving Custom Field to database
===

   <p> I wrote a very simple plugin to add custom fields to media library but in the database wp_postmeta table shows that there is no meta data for my pdf. I am supposed to get serialized meta data in the meta_value column. Is my plugin incorrect below? 
The plugin achieves adding the custom fields but not saving to the database.</p>
![enter image description here][1]


    meta_id post_id	    meta_value
    552	  356	       a:0:{}
    551	  356	
  

<h1>Plugin Code</h1> 
      <?php
        /*
        Plugin Name: Media Library Fields
        Plugin URI: http://mhmintranet
        Description: The plugin adds additional fields to the media library
        Version: 1.0
        Author: me
        Author URI: Metropolitan State Hospital http://mhmintranet
        License: GPL2
        */
        function GetCustomFormFields($form_fields, $post)
        {
        	$form_fields['RevisionDate'] = array(
        			
        			'label' => 'Revision Date',
        			'input' => 'text',
        			'value' => get_post_meta($posdt->ID, '_RevisionDate',true),
        			'helps' => 'This is the date the document was revised last'
        			);
        			
        	$form_fields['ADTitle'] = array(
        			
        			'label' => 'AD Title',
        			'input' => 'text',
        			'value' => get_post_meta($posdt->ID, '_ADTitle',true),
        			'helps' => 'Administrative Directive Title'
        			);
        	$form_fields['AdNumber'] = array(
        			
        			'label' => 'AD Number',
        			'input' => 'text',
        			'value' => get_post_meta($posdt->ID, '_AdNumber',true),
        			'helps' => 'Administrative Directive Title'
        			);
        	
        	return $form_fields;
        }
        add_filter("attachment_fields_to_edit", "GetCustomFormFields", null, 2);  
        
        function SaveCustomFormFields($post,$attachment)
        {
        	if(isset($attachment['RevisionDate']))
        	{
        		update_post_meta($post['ID'], '_RevisionDate', $attachment['RevisionDate']);  
        	}
        if(isset($attachment['ADTitle']))
        	{
        		update_post_meta($post['ID'], '_ADTitle', $attachment['ADTitle']);  
        	}
        if(isset($attachment['AdNumber']))
        	{
        		update_post_meta($post['ID'], '_AdNumber', $attachment['AdNumber']);  
        	}
        	return $post;
        }
        add_filter('attachment_fields_to_save','SaveCustomFormFields');
        
        ?>


  [1]: http://i.stack.imgur.com/HkNIl.png