Magento Products Comparison limit

I need to limit the number 开发者_Go百科of products added to compare in Magento. Only wanted to have a maximum of 4 products to be compared.

I'm thinking of doing it in the .phtml (where item display looping is) but have no idea where I should edit to display the message "Compare list is full". Any idea?

Thanks!

I've hooked to the catalog_product_compare_add_product event.

Here is my solution:

1. Create module.

   Directories:

   app/code/local/Company //this can be any name

   app/code/local/Company/Catalog

   app/code/local/Company/Catalog/Helper

   app/code/local/Company/Catalog/etc

2. Module config

   Create a file: app/code/local/Company/Catalog/etc/config.xml

   File contents:

   <?xml version="1.0"?>
   <config>
       <modules>
           <Company_Catalog>
               <version>0.1</version>
           </Company_Catalog>
       </modules>
       <frontend>
           <events>
               <catalog_product_compare_add_product>
                   <observers>
                       <company_catalog>
                           <type>singleton</type>
                           <class>Company_Catalog_Helper_Observer</class>
                           <method>limitProductCompare</method>
                       </company_catalog>
                   </observers>
               </catalog_product_compare_add_product>
           </events>
       </frontend>
   </config>
   

3. Helper

   Create a file: app/code/local/Company/Catalog/Helper/Observer.php

   File contents:

   <?php
   
   class Company_Catalog_Helper_Observer extends Mage_Catalog_Helper_Data {
   
       const COMPARE_LIMIT = 4;
   
       function limitProductCompare($event) {
           if (Mage::helper('catalog/product_compare')->getItemCount()<self::COMPARE_LIMIT) return;
   
           $session = Mage::getSingleton('catalog/session');
           Mage::getSingleton('catalog/product_compare_list')->removeProduct($event->getProduct());
   
           $session->getMessages()->clear();
           $session->addNotice($this->__('You have reached the limit of products to compare. Remove one and try again.'));
       } 
   
   } 
   

4. Enable module

   Create file: app/etc/modules/Company_Catalog.xml

   File contents:

   <?xml version="1.0" encoding="UTF-8"?>
   <config>
       <modules>
           <Company_Catalog>
               <active>true</active>
               <codePool>local</codePool>
           </Company_Catalog>
       </modules>
   </config>
   

5. Profit!

   Everything should work fine now. After adding, 5th product gets removed, and nice notice is displayed. Its not the perfect solution (since it removes a product after it was added), but it does the job well.

compare items are added in Mage_Catalog_Product_CompareController and you can see that there are events dispatched that you can hook your observer to or you can add your limits by extending Mage_Catalog_Model_Product_Compare_List and overriding addProduct() or addProducts() methods or even make this in collection classes