title: Unable to add canonical tag in opencart
body: <p>For some strange reason I am unable to add the canonical tag to opencart 1.5.2.1 product pages and category pages. I've made changes to both product.php and category.php but it just doesn't show up in View Source. Can anyone let me know if I missed out something?</p>
  
  <p>Files Edited</p>
  
  <p>1) catalog/controller/product/product.php
  2) catalog/controller/product/category.php</p>
  
  <p>Code added</p>
  
  <pre><code>$this-&gt;document-&gt;addLink($this-&gt;url-&gt;link('product/category', 'path=' . $category_id), 'canonical');
  </code></pre>
  
  <p>after</p>
  
  <pre><code>$this-&gt;document-&gt;setKeywords($product_info['meta_keyword']);
  </code></pre>