how to add new custom field virtuemart product category fields in joomla administrator

how to add new field from category virtuemart joomla
execute query for add new category fields
1stp->   ALTER TABLE `jos_vm_category` ADD ` cat_wholesaler` VARCHAR( 1 ) NOT NULL DEFAULT 'N' AFTER `products_per_row` ;

2stp-> GO TO D:\xampp\htdocs\mil-bar\administrator\components\com_virtuemart\html\product.product_category_form.php open
add your field in product.product_category_form.php

      if ($db->sf("cat_wholesaler")=="Y")
         {
          echo "<input type=\"checkbox\" name=\"accesscat\" value=\"Y\" checked=\"checked\" />";
         }else{
          echo "<input type=\"checkbox\" name=\"accesscat\" value=\"Y\" />";
         }

2stp->  administrator/components/com_virtuemart/classes/ps_product_category.php in (function add( &$d ))

a. first get new field value for insert paste below code line 253

      if (vmGet($d,'accesscat')==''){
                 $waccess='N';
        }else{
                 $waccess='Y';
              }

$fields = array('vendor_id' => $ps_vendor_id,
    'category_name' => vmGet( $d, 'category_name' ),
    'category_publish' => vmGet( $d, 'category_publish' ),
    'category_description' => vmGet( $d, 'category_description', '',VMREQUEST_ALLOWHTML ),
        'category_browsepage' => vmGet( $d, 'category_browsepage' ),
    'products_per_row' => vmRequest::getInt( 'products_per_row' ),
    'cat_wholesaler'=>$waccess,
    'category_flypage' => vmGet( $d, 'category_flypage' ),
    'category_thumb_image' => vmGet( $d, 'category_thumb_image' ),
    'category_full_image' => vmGet( $d, 'category_full_image' ),
    'cdate' => $timestamp,
    'mdate' => $timestamp,
    'list_order' => $list_order,
    );

b. for update field value from database same page line  315(function update(&$d))

                       if (vmGet($d,'accesscat')=='')
                          {
                 $waccess='N';
              }else{
                 $waccess='Y';
              }

$fields = array('category_name' => vmGet( $d, 'category_name' ),
           'category_publish' => vmGet( $d, 'category_publish' ),
           'category_description' => vmGet( $d, 'category_description', '',VMREQUEST_ALLOWHTML ),
       'category_browsepage' => vmGet( $d, 'category_browsepage' ),
                                        'products_per_row' => vmRequest::getInt( 'products_per_row' ),
                                        'cat_wholesaler'=> $waccess,
                                        'category_flypage' => vmGet( $d, 'category_flypage' ),
                                        'category_thumb_image' => vmGet( $d, 'category_thumb_image' ),
                                        'category_full_image' => vmGet( $d, 'category_full_image' ),
                                        'mdate' => $timestamp,
                                        'list_order' => vmRequest::getInt('list_order'),
                                    );


lastly enloy your custom field has been added you can insert value and update successfully in virtuemart