Override PrestaShop Class with additional fields

altertable.sql

ALTER TABLE `PREFIX_product` ADD `custom_field` varchar(255);

informations.tpl

{*
* 2007-2013 PrestaShop
*
* NOTICE OF LICENSE
*
* This source file is subject to the Academic Free License (AFL 3.0)
* that is bundled with this package in the file LICENSE.txt.
* It is also available through the world-wide-web at this URL:
* http://opensource.org/licenses/afl-3.0.php
* If you did not receive a copy of the license and are unable to
* obtain it through the world-wide-web, please send an email
* to license@prestashop.com so we can send you a copy immediately.
*
* DISCLAIMER
*
* Do not edit or add to this file if you wish to upgrade PrestaShop to newer
* versions in the future. If you wish to customize PrestaShop for your
* needs please refer to http://www.prestashop.com for more information.
*
*  @author PrestaShop SA <contact@prestashop.com>
*  @copyright  2007-2013 PrestaShop SA
*  @license    http://opensource.org/licenses/afl-3.0.php  Academic Free License (AFL 3.0)
*  International Registered Trademark & Property of PrestaShop SA
*}
{if $check_product_association_ajax}
{assign var=class_input_ajax value='check_product_name '}
{else}
{assign var=class_input_ajax value=''}
{/if}
<input type="hidden" name="submitted_tabs[]" value="Informations" />
<div id="step1">
  <h4 class="tab">1. {l s='Info.'}</h4>
	<h4>{l s='Product global information'}</h4>
	<script type="text/javascript">
		{if isset($PS_ALLOW_ACCENTED_CHARS_URL) && $PS_ALLOW_ACCENTED_CHARS_URL}
			var PS_ALLOW_ACCENTED_CHARS_URL = 1;
		{else}
			var PS_ALLOW_ACCENTED_CHARS_URL = 0;
		{/if}
		{$combinationImagesJs}
		{if $check_product_association_ajax}
				var search_term = '';
				$('document').ready( function() {
					$(".check_product_name")
						.autocomplete(
							'{$link->getAdminLink('AdminProducts', true)|addslashes}', {
								minChars: 3,
								max: 10,
								width: $(".check_product_name").width(),
								selectFirst: false,
								scroll: false,
								dataType: "json",
								formatItem: function(data, i, max, value, term) {
									search_term = term;
									// adding the little
									if ($('.ac_results').find('.separation').length == 0)
										$('.ac_results').css('background-color', '#EFEFEF')
											.prepend('<div style="color:#585A69; padding:2px 5px">{l s='Use a product from the list'}<div class="separation"></div></div>');
									return value;
								},
								parse: function(data) {
									var mytab = new Array();
									for (var i = 0; i < data.length; i++)
										mytab[mytab.length] = { data: data[i], value: data[i].name };
									return mytab;
								},
								extraParams: {
									ajax: 1,
									action: 'checkProductName',
									id_lang: {$id_lang}
								}
							}
						)
						.result(function(event, data, formatted) {
							// keep the searched term in the input
							$('#name_{$id_lang}').val(search_term);
							jConfirm('{l s='Do you want to use this product?'}&nbsp;<strong>'+data.name+'</strong>', '{l s='Confirmation'}', function(confirm){
								if (confirm == true)
									document.location.href = '{$link->getAdminLink('AdminProducts', true)}&updateproduct&id_product='+data.id_product;
								else
									return false;
							});
						});
				});
		{/if}
	</script>

	{if isset($display_common_field) && $display_common_field}
		<div class="warn" style="display: block">{l s='Warning, if you change the value of fields with an orange bullet %s, the value will be changed for all other shops for this product' sprintf=$bullet_common_field}</div>
	{/if}

	{include file="controllers/products/multishop/check_fields.tpl" product_tab="Informations"}

	<div class="separation"></div>
	<div id="warn_virtual_combinations" class="warn" style="display:none">{l s='You cannot use combinations with a virtual product.'}</div>
	<div>
		<label class="text">{$bullet_common_field} {l s='Type:'}</label>
		<input type="radio" name="type_product" id="simple_product" value="{Product::PTYPE_SIMPLE}" {if $product_type == Product::PTYPE_SIMPLE}checked="checked"{/if} />
		<label class="radioCheck" for="simple_product">{l s='Product'}</label>
		<input type="radio" name="type_product" {if $is_in_pack}disabled="disabled"{/if} id="pack_product" value="{Product::PTYPE_PACK}" {if $product_type == Product::PTYPE_PACK}checked="checked"{/if} />
		<label class="radioCheck" for="pack_product">{l s='Pack'}</label>
		<input type="radio" name="type_product" id="virtual_product" {if $is_in_pack}disabled="disabled"{/if} value="{Product::PTYPE_VIRTUAL}" {if $product_type == Product::PTYPE_VIRTUAL}checked="checked"{/if} />
		<label class="radioCheck" for="virtual_product">{l s='Virtual Product (services, booking or downloadable products)'}</label>
	</div>

	<div class="separation"></div>
	<br />
	<table cellpadding="5" style="width: 50%; float: left; margin-right: 20px; border-right: 1px solid #CCCCCC;">
	{* global information *}
		<tr>
			<td class="col-left">
				{include file="controllers/products/multishop/checkbox.tpl" field="name" type="default" multilang="true"}
				<label>{l s='Name:'}</label>
			</td>
			<td style="padding-bottom:5px;" class="translatable">
			{foreach from=$languages item=language}
				<div class="lang_{$language.id_lang}" style="{if !$language.is_default}display: none;{/if} float: left;">
						<input class="{$class_input_ajax}{if !$product->id}copy2friendlyUrl{/if} updateCurrentText" size="43" type="text" {if !$product->id}disabled="disabled"{/if}
						id="name_{$language.id_lang}" name="name_{$language.id_lang}"
						value="{$product->name[$language.id_lang]|htmlentitiesUTF8|default:''}"/><sup> *</sup>
					<span class="hint" name="help_box">{l s='Invalid characters:'} <>;=#{}<span class="hint-pointer">&nbsp;</span>
					</span>
				</div>
			{/foreach}
			</td>
		</tr>
    <tr>
  		<td class="col-left"><label>{l s='Custom field:'}</label></td>
			<td style="padding-bottom:5px;">
				<input size="55" type="text" name="custom_field" value="{$product->custom_field}" style="width: 130px; margin-right: 44px;" />
			</td>
		</tr>
		<tr>
			<td class="col-left"><label>{$bullet_common_field} {l s='Reference:'}</label></td>
			<td style="padding-bottom:5px;">
				<input size="55" type="text" name="reference" value="{$product->reference|htmlentitiesUTF8}" style="width: 130px; margin-right: 44px;" />
				<span class="hint" name="help_box">{l s='Special characters allowed:'}.-_#\<span class="hint-pointer">&nbsp;</span></span>
			</td>
		</tr>
		<tr>
			<td class="col-left"><label>{$bullet_common_field} {l s='EAN13 or JAN:'}</label></td>
			<td style="padding-bottom:5px;">
				<input size="55" maxlength="13" type="text" name="ean13" value="{$product->ean13|htmlentitiesUTF8}" style="width: 130px; margin-right: 5px;" /> <span class="small">{l s='(Europe, Japan)'}</span>
			</td>
		</tr>
		<tr>
			<td class="col-left"><label>{$bullet_common_field} {l s='UPC:'}</label></td>
			<td style="padding-bottom:5px;">
				<input size="55" maxlength="12" type="text" name="upc" value="{$product->upc|escape:html:'UTF-8'}" style="width: 130px; margin-right: 5px;" /> <span class="small">{l s='(US, Canada)'}</span>
			</td>
		</tr>
	</table>
	{* status informations *}
	<table cellpadding="5" style="width: 40%; float: left; margin-left: 10px;">
	<tr>
		<td class="col-left">
			{include file="controllers/products/multishop/checkbox.tpl" field="active" type="radio" onclick=""}
			<label class="text">{l s='Status:'}</label>
		</td>
		<td style="padding-bottom:5px;">
			<ul class="listForm">
				<li>
					<input onclick="toggleDraftWarning(false);showOptions(true);showRedirectProductOptions(false);" type="radio" name="active" id="active_on" value="1" {if $product->active || !$product->isAssociatedToShop()}checked="checked" {/if} />
					<label for="active_on" class="radioCheck">{l s='Enabled'}</label>
				</li>
				<li>
					<input onclick="toggleDraftWarning(true);showOptions(false);showRedirectProductOptions(true);"  type="radio" name="active" id="active_off" value="0" {if !$product->active && $product->isAssociatedToShop()}checked="checked"{/if} />
					<label for="active_off" class="radioCheck">{l s='Disabled'}</label>
				</li>
			</ul>
		</td>
	</tr>
	<tr class="redirect_product_options" style="display:none">
		<td class="col-left">
			{include file="controllers/products/multishop/checkbox.tpl" field="active" type="radio" onclick=""}
			<label class="text">{l s='Redirect:'}</label>
		</td>
		<td style="padding-bottom:5px;">
			<select name="redirect_type" id="redirect_type">
				<option value="404" {if $product->redirect_type == '404'} selected="selected" {/if}>{l s='No redirect (404)'}</option>
				<option value="301" {if $product->redirect_type == '301'} selected="selected" {/if}>{l s='Redirect permanently (301)'}</option>
				<option value="302" {if $product->redirect_type == '302'} selected="selected" {/if}>{l s='Redirect temporarily (302)'}</option>
			</select>
			<span class="hint" name="help_box">
				{l s='404 : Not Found = Product does not exist and no redirect'}<br/>
				{l s='301 : Moved Permanently = Product Moved Permanently'}<br/>
				{l s='302 : Moved Temporarily = Product moved temporarily'}
			</span>
		</td>
	</tr>
	<tr class="redirect_product_options redirect_product_options_product_choise" style="display:none">
		<td class="col-left">
			{include file="controllers/products/multishop/checkbox.tpl" field="active" type="radio" onclick=""}
			<label class="text">{l s='Related product:'}</label>
		</td>
		<td style="padding-bottom:5px;">
			<input type="hidden" value="" name="id_product_redirected" />
			<input value="" id="related_product_autocomplete_input" autocomplete="off" class="ac_input" />
			<p>
				<script>
					var no_related_product = '{l s='No related product'}';
					var id_product_redirected = {$product->id_product_redirected|intval};
					var product_name_redirected = '{$product_name_redirected|escape:html:'UTF-8'}';
				</script>
				<span id="related_product_name">{l s='No related product'}</span>
				<span id="related_product_remove" style="display:none">
					<a hre="#" onclick="removeRelatedProduct(); return false" id="related_product_remove_link">
						<img src="../img/admin/delete.gif" class="middle" alt="" />
					</a>
				</span>
			</p>
		</td>
	</tr>
	<tr>
		<td class="col-left">
			{include file="controllers/products/multishop/checkbox.tpl" field="visibility" type="default"}
			<label>{l s='Visibility:'}</label>
		</td>
		<td style="padding-bottom:5px;">
			<select name="visibility" id="visibility">
				<option value="both" {if $product->visibility == 'both'}selected="selected"{/if} >{l s='Everywhere'}</option>
				<option value="catalog" {if $product->visibility == 'catalog'}selected="selected"{/if} >{l s='Catalog only'}</option>
				<option value="search" {if $product->visibility == 'search'}selected="selected"{/if} >{l s='Search only'}</option>
				<option value="none" {if $product->visibility == 'none'}selected="selected"{/if}>{l s='Nowhere'}</option>
			</select>
		</td>
	</tr>
	<tr id="product_options" {if !$product->active}style="display:none"{/if} >
		<td class="col-left">
			{if isset($display_multishop_checkboxes) && $display_multishop_checkboxes}
				<div class="multishop_product_checkbox">
					<ul class="listForm">
						<li>{include file="controllers/products/multishop/checkbox.tpl" only_checkbox="true" field="available_for_order" type="default"}</li>
						<li>{include file="controllers/products/multishop/checkbox.tpl" only_checkbox="true" field="show_price" type="show_price"}</li>
						<li>{include file="controllers/products/multishop/checkbox.tpl" only_checkbox="true" field="online_only" type="default"}</li>
					</ul>
				</div>
			{/if}

			<label>{l s='Options:'}</label>
		</td>
		<td style="padding-bottom:5px;">
			<ul class="listForm">
				<li>
					<input  type="checkbox" name="available_for_order" id="available_for_order" value="1" {if $product->available_for_order}checked="checked"{/if}  />
					<label for="available_for_order" class="t">{l s='Available for order'}</label>
				</li>
			<li>
				<input type="checkbox" name="show_price" id="show_price" value="1" {if $product->show_price}checked="checked"{/if} {if $product->available_for_order}disabled="disabled"{/if}/>
				<label for="show_price" class="t">{l s='show price'}</label>
			</li>
			<li>
				<input type="checkbox" name="online_only" id="online_only" value="1" {if $product->online_only}checked="checked"{/if} />
				<label for="online_only" class="t">{l s='Online only (not sold in store)'}</label>
			</li>
			</ul>
		</td>
	</tr>
	<tr>
		<td class="col-left">
			{include file="controllers/products/multishop/checkbox.tpl" field="condition" type="default"}
			<label>{l s='Condition:'}</label>
		</td>
		<td style="padding-bottom:5px;">
			<select name="condition" id="condition">
				<option value="new" {if $product->condition == 'new'}selected="selected"{/if} >{l s='New'}</option>
				<option value="used" {if $product->condition == 'used'}selected="selected"{/if} >{l s='Used'}</option>
				<option value="refurbished" {if $product->condition == 'refurbished'}selected="selected"{/if}>{l s='Refurbished'}</option>
			</select>
		</td>
	</tr>
</table>

<table cellpadding="5" cellspacing="0" border="0" style="width: 100%;"><tr><td><div class="separation"></div></td></tr></table>
		<table cellspacing="0" cellpadding="5" border="0">
			<tr>
				<td class="col-left">
					{include file="controllers/products/multishop/checkbox.tpl" field="description_short" type="tinymce" multilang="true"}
					<label>{l s='Short description:'}<br /></label>
					<p class="product_description">({l s='Appears in the product list(s), and on the top of the product page.'})</p>
				</td>
				<td style="padding-bottom:5px;">
						{include file="controllers/products/textarea_lang.tpl"
						languages=$languages
						input_name='description_short'
						input_value=$product->description_short
						max=$PS_PRODUCT_SHORT_DESC_LIMIT}
					<p class="clear"></p>
				</td>
			</tr>
			<tr>
				<td class="col-left">
					{include file="controllers/products/multishop/checkbox.tpl" field="description" type="tinymce" multilang="true"}
					<label>{l s='Description:'}<br /></label>
					<p class="product_description">({l s='Appears in the body of the product page'})</p>
				</td>
				<td style="padding-bottom:5px;">
						{include file="controllers/products/textarea_lang.tpl" languages=$languages
						input_name='description'
						input_value=$product->description
						}
					<p class="clear"></p>
				</td>
			</tr>
		{if $images}
			<tr>
				<td class="col-left"><label></label></td>
				<td style="padding-bottom:5px;">
					<div style="display:block;width:620px;" class="hint clear">
						{l s='Do you want an image associated with the product in your description?'}
						<span class="addImageDescription" style="cursor:pointer">{l s='Click here'}</span>.
					</div>
					<p class="clear"></p>
				</td>
			</tr>
			</table>
				<table id="createImageDescription" style="display:none;width:100%">
					<tr>
						<td colspan="2" height="10"></td>
					</tr>
					<tr>
						<td class="col-left"><label>{l s='Select your image:'}</label></td>
						<td style="padding-bottom:5px;">
							<ul class="smallImage">
							{foreach from=$images item=image key=key}
									<li>
										<input type="radio" name="smallImage" id="smallImage_{$key}" value="{$image.id_image}" {if $key == 0}checked="checked"{/if} >
										<label for="smallImage_{$key}" class="t">
											<img src="{$image.src}" alt="{$image.legend}" />
										</label>
									</li>
							{/foreach}
							</ul>
							<p class="clear"></p>
						</td>
					</tr>
					<tr>
						<td class="col-left"><label>{l s='Position:'}</label></td>
						<td style="padding-bottom:5px;">
							<ul class="listForm">
								<li><input type="radio" name="leftRight" id="leftRight_1" value="left" checked>
									<label for="leftRight_1" class="t">{l s='left'}</label>
								</li>
								<li>
									<input type="radio" name="leftRight" id="leftRight_2" value="right">
									<label for="leftRight_2" class="t">{l s='right'}</label>
								</li>
							</ul>
						</td>
					</tr>
					<tr>
						<td class="col-left"><label>{l s='Select the type of picture:'}</label></td>
						<td style="padding-bottom:5px;">
							<ul class="listForm">
							{foreach from=$imagesTypes key=key item=type}
								<li><input type="radio" name="imageTypes" id="imageTypes_{$key}" value="{$type.name}" {if $key == 0}checked="checked"{/if}>
									<label for="imageTypes_{$key}" class="t">{$type.name} <span>({$type.width}px {l s='by'} {$type.height}px)</span></label>
								</li>
							{/foreach}
							</ul>
							<p class="clear"></p>
						</td>
					</tr>
					<tr>
						<td class="col-left"><label>{l s='Image tag to insert:'}</label></td>
						<td style="padding-bottom:5px;">
							<input type="text" id="resultImage" name="resultImage" />
							<p class="preference_description">{l s='The tag to copy/paste into the description.'}</p>
						</td>
					</tr>
					<tr>
						<td colspan="2">
							<div class="separation"></div>
						</td>
					</tr>
				</table>
		{/if}
		<table>
		<tr>
			<td class="col-left"><label>{l s='Tags:'}</label></td>
			<td style="padding-bottom:5px;" class="translatable">
				{foreach from=$languages item=language}
					<div class="lang_{$language.id_lang}" style="{if !$language.is_default}display: none;{/if}float: left;">
						<input size="55" type="text" id="tags_{$language.id_lang}" name="tags_{$language.id_lang}"
							value="{$product->getTags($language.id_lang, true)|htmlentitiesUTF8}" />
						<span class="hint" name="help_box">{l s='Forbidden characters:'} !&lt;;&gt;;?=+#&quot;&deg;{}_$%<span class="hint-pointer">&nbsp;</span></span>
					</div>
				{/foreach}
				<p class="preference_description clear">{l s='Tags separated by commas (e.g. dvd, dvd player, hifi)'}</p>
			</td>
		</tr>
		</table>
	</table>
	<br />
</div>

Product.php

class Product extends ProductCore
{
  	public $custom_field;
	
	public function __construct($id_product = null, $full = false, $id_lang = null, $id_shop = null, Context $context = null)
	{
		self::$definition['fields']['custom_field'] = array('type' => self::TYPE_STRING, 'shop' => false, 'validate' => 'isString');
		parent::__construct($id_product, $full, $id_lang, $id_shop, $context);
	}
		
		
}

Product.php => override/classes/Product.php
informations.tpl => override/controller/admin/templates/products/informations.tpl
altertable.sql => phpMyAdmin table PREFIX_product => SQL tab

• remember to delete cache/class_index.php
• remember to change PREFIX