Admin Panel – How to Add Tab to Product Information

Assuming you already have your entity and a grid for it in the backend here is what you need. In my example, my entity is called article and the module is Easylife_Press. Adjust the names to fit your module.

First you need a new table to remember the relation between products and your entities. For this add in your config.xml the table declaration inside the resource model tag. (models->press->press_resource->entities)

<article_product><!-- relation table -->
     <table>press_article_product</table>
</article_product>

Now you need to create the table. In one of your upgrade scripts add this:

$this->run("
    CREATE TABLE {$this->getTable('press/article_product')} (
        `rel_id` int(11) unsigned NOT NULL auto_increment,
        `article_id` int(11) unsigned NOT NULL,
        `product_id` int(11) unsigned NOT NULL,
        `position` int(11) unsigned NOT NULL default '0',
    PRIMARY KEY  (`rel_id`),
    UNIQUE KEY `UNIQUE_ARTICLE_PRODUCT` (`article_id`,`product_id`),
    CONSTRAINT `PRESS_ARTICLE_ARTICLE_PRODUCT` FOREIGN KEY (`article_id`) REFERENCES {$this->getTable('press/article')} (`entity_id`) ON DELETE CASCADE ON UPDATE CASCADE,
    CONSTRAINT `PRESS_ARTICLE_PRODUCT_ARTICLE` FOREIGN KEY (`product_id`) REFERENCES {$this->getTable('catalog_product_entity')} (`entity_id`) ON DELETE CASCADE ON UPDATE CASCADE
    )
    ENGINE=InnoDB DEFAULT CHARSET=utf8;
");

If the PK of your entity table is not entity_id change it. Sorry that I don't have the DDL install script. It's easier to understand this way. If you want I will write one.

Now you need a model to handle this table. app/code/local/Easylife/Press/Model/Article/Product.php

<?php 
class Easylife_Press_Model_Article_Product extends Mage_Core_Model_Abstract{
    protected function _construct(){
        $this->_init('press/article_product');
    }
    /**
     * Save data for article-product relation
     * @access public
     * @param  Easylife_Press_Model_Article $article
     * @return Easylife_Press_Model_Article_Product
     * 
     */
    public function saveArticleRelation($article){
        $data = $article->getProductsData();
        if (!is_null($data)) {
            $this->_getResource()->saveArticleRelation($article, $data);
        }
        return $this;
    }
    /**
     * get products for article
     * @access public
     * @param Easylife_Press_Model_Article $article
     * @return Easylife_Press_Model_Resource_Article_Product_Collection
     * 
     */
    public function getProductCollection($article){
        $collection = Mage::getResourceModel('press/article_product_collection')
            ->addArticleFilter($article);
        return $collection;
    }
}

And a model that maps on a table requires a resource model.
app/code/local/Easylife/Press/Model/Resource/Article/Product.php

<?php 
class Easylife_Press_Model_Resource_Article_Product extends Mage_Core_Model_Resource_Db_Abstract{
    /**
     * initialize resource model
     * @access protected
     * @return void
     * @see Mage_Core_Model_Resource_Abstract::_construct()
     * 
     */
    protected function  _construct(){
        $this->_init('press/article_product', 'rel_id');
    }
    /**
     * Save article - product relations
     * @access public
     * @param Easylife_Press_Model_Article $article
     * @param array $data
     * @return Easylife_Press_Model_Resource_Article_Product
     * 
     */
    public function saveArticleRelation($article, $data){
        if (!is_array($data)) {
            $data = array();
        }
        $deleteCondition = $this->_getWriteAdapter()->quoteInto('article_id=?', $article->getId());
        $this->_getWriteAdapter()->delete($this->getMainTable(), $deleteCondition);

        foreach ($data as $productId => $info) {
            $this->_getWriteAdapter()->insert($this->getMainTable(), array(
                'article_id'      => $article->getId(),
                'product_id'     => $productId,
                'position'      => @$info['position']
            ));
        }
        return $this;
    }
    /**
     * Save  product - article relations
     * @access public
     * @param Mage_Catalog_Model_Product $prooduct
     * @param array $data
     * @return Easylife_Press_Model_Resource_Article_Product
     * @
     */
    public function saveProductRelation($product, $data){
        if (!is_array($data)) {
            $data = array();
        }
        $deleteCondition = $this->_getWriteAdapter()->quoteInto('product_id=?', $product->getId());
        $this->_getWriteAdapter()->delete($this->getMainTable(), $deleteCondition);

        foreach ($data as $articleId => $info) {
            $this->_getWriteAdapter()->insert($this->getMainTable(), array(
                'article_id' => $articleId,
                'product_id' => $product->getId(),
                'position'   => @$info['position']
            ));
        }
        return $this;
    }
}

...and a collection resource model:
app/code/local/Easylife/Press/Model/Resource/Article/Product/Collection.php

<?php 
class Easylife_Press_Model_Resource_Article_Product_Collection extends Mage_Catalog_Model_Resource_Product_Collection{
    /**
     * remember if fields have been joined
     * @var bool
     */
    protected $_joinedFields = false;
    /**
     * join the link table
     * @access public
     * @return Easylife_Press_Model_Resource_Article_Product_Collection
     * 
     */
    public function joinFields(){
        if (!$this->_joinedFields){
            $this->getSelect()->join(
                array('related' => $this->getTable('press/article_product')),
                'related.product_id = e.entity_id',
                array('position')
            );
            $this->_joinedFields = true;
        }
        return $this;
    }
    /**
     * add article filter
     * @access public
     * @param Easylife_Press_Model_Article | int $article
     * @return Easylife_Press_Model_Resource_Article_Product_Collection
     * 
     */
    public function addArticleFilter($article){
        if ($article instanceof Easylife_Press_Model_Article){
            $article = $article->getId();
        }
        if (!$this->_joinedFields){
            $this->joinFields();
        }
        $this->getSelect()->where('related.article_id = ?', $article);
        return $this;
    }
}

Then you need to add a new tab in the product add/edit form and save the values from it. For this you need to observe the event core_block_abstract_prepare_layout_after. Add the following to your config.xml file inside the <adminhtml> tag.

<events>
    <core_block_abstract_prepare_layout_after> <!-- this will add the tab-->
        <observers>
            <article>
                <type>singleton</type>
                <class>press/adminhtml_observer</class>
                <method>addArticleBlock</method>
            </article>
        </observers>
    </core_block_abstract_prepare_layout_after>
    <catalog_product_save_after><!-- this will save the relations -->
        <observers>
            <article>
                <type>singleton</type>
                <class>press/adminhtml_observer</class>
                <method>saveArticleData</method>
            </article>
        </observers>
    </catalog_product_save_after>
</events>

Now the observer that adds the tab and saves the relations
app/code/local/Easylife/Press/Model/Adminhtml/Observer.php

<?php
class Easylife_Press_Model_Adminhtml_Observer{
    /**
     * check if tab can be added
     * @access protected
     * @param Mage_Catalog_Model_Product $product
     * @return bool
     * 
     */
    protected function _canAddTab($product){
        if ($product->getId()){
            return true;
        }
        if (!$product->getAttributeSetId()){
            return false;
        }
        $request = Mage::app()->getRequest();
        if ($request->getParam('type') == 'configurable'){
            if ($request->getParam('attribtues')){
                return true;
            }
        }
        return false;
    }
    /**
     * add the article tab to products
     * @access public
     * @param Varien_Event_Observer $observer
     * @return Easylife_Press_Model_Adminhtml_Observer
     * 
     */
    public function addArticleBlock($observer){
        $block = $observer->getEvent()->getBlock();
        $product = Mage::registry('product');
        if ($block instanceof Mage_Adminhtml_Block_Catalog_Product_Edit_Tabs && $this->_canAddTab($product)){
            $block->addTab('articles', array(
                'label' => Mage::helper('press')->__('Articles'),
                'url'   => Mage::helper('adminhtml')->getUrl('adminhtml/press_article_catalog_product/articles', array('_current' => true)),
                'class' => 'ajax',
            ));
        }
        return $this;
    }
    /**
     * save article - product relation
     * @access public
     * @param Varien_Event_Observer $observer
     * @return Easylife_Press_Model_Adminhtml_Observer
     * 
     */
    public function saveArticleData($observer){
        $post = Mage::app()->getRequest()->getPost('articles', -1);
        if ($post != '-1') {
            $post = Mage::helper('adminhtml/js')->decodeGridSerializedInput($post);
            $product = Mage::registry('product');
            $articleProduct = Mage::getResourceSingleton('press/article_product')->saveProductRelation($product, $post);
        }
        return $this;
    }
}

One helper to make it easier to get the related entities app/code/local/Easylife/Press/Helper/Product.php:

<?php
class Easylife_Press_Helper_Product extends Easylife_Press_Helper_Data{
    /**
     * get the selected articles for a product
     * @access public
     * @param Mage_Catalog_Model_Product $product
     * @return array()
     * 
     */
    public function getSelectedArticles(Mage_Catalog_Model_Product $product){
        if (!$product->hasSelectedArticles()) {
            $articles = array();
            foreach ($this->getSelectedArticlesCollection($product) as $article) {
                $articles[] = $article;
            }
            $product->setSelectedArticles($articles);
        }
        return $product->getData('selected_articles');
    }
    /**
     * get article collection for a product
     * @access public
     * @param Mage_Catalog_Model_Product $product
     * @return Easylife_Press_Model_Resource_Article_Collection
     */
    public function getSelectedArticlesCollection(Mage_Catalog_Model_Product $product){
        $collection = Mage::getResourceSingleton('press/article_collection')
            ->addProductFilter($product);
        return $collection;
    }
}

Now the actual grid block. app/code/local/Easylife/Press/Block/Adminhtml/Catalog/Product/Edit/Tab/Article.php

<?php
class Easylife_Press_Block_Adminhtml_Catalog_Product_Edit_Tab_Article extends Mage_Adminhtml_Block_Widget_Grid {
    /**
     * Set grid params
     * @access protected
     * @return void
     * 
     */
    public function __construct(){
        parent::__construct();
        $this->setId('article_grid');
        $this->setDefaultSort('position');
        $this->setDefaultDir('ASC');
        $this->setUseAjax(true);
        if ($this->getProduct()->getId()) {
            $this->setDefaultFilter(array('in_articles'=>1));
        }
    }
    /**
     * prepare the article collection
     * @access protected 
     * @return Easylife_Press_Block_Adminhtml_Catalog_Product_Edit_Tab_Article
     * 
     */
    protected function _prepareCollection() {
        $collection = Mage::getResourceModel('press/article_collection');
        if ($this->getProduct()->getId()){
            $constraint = 'related.product_id='.$this->getProduct()->getId();
            }
            else{
                $constraint = 'related.product_id=0';
            }
        $collection->getSelect()->joinLeft(
            array('related'=>$collection->getTable('press/article_product')),
            'related.article_id=main_table.entity_id AND '.$constraint,
            array('position')
        );
        $this->setCollection($collection);
        parent::_prepareCollection();
        return $this;
    }
    /**
     * prepare mass action grid
     * @access protected
     * @return Easylife_Press_Block_Adminhtml_Catalog_Product_Edit_Tab_Article
     * 
     */ 
    protected function _prepareMassaction(){
        return $this;
    }
    /**
     * prepare the grid columns
     * @access protected
     * @return Easylife_Press_Block_Adminhtml_Catalog_Product_Edit_Tab_Article
     * 
     */
    protected function _prepareColumns(){
        $this->addColumn('in_articles', array(
            'header_css_class'  => 'a-center',
            'type'  => 'checkbox',
            'name'  => 'in_articles',
            'values'=> $this->_getSelectedArticles(),
            'align' => 'center',
            'index' => 'entity_id'
        ));
        $this->addColumn('title', array(
            'header'=> Mage::helper('press')->__('Title'),
            'align' => 'left',
            'index' => 'title',
        ));
        $this->addColumn('position', array(
            'header'        => Mage::helper('press')->__('Position'),
            'name'          => 'position',
            'width'         => 60,
            'type'        => 'number',
            'validate_class'=> 'validate-number',
            'index'         => 'position',
            'editable'      => true,
        ));
    }
    /**
     * Retrieve selected articles
     * @access protected
     * @return array
     * 
     */
    protected function _getSelectedArticles(){
        $articles = $this->getProductArticles();
        if (!is_array($articles)) {
            $articles = array_keys($this->getSelectedArticles());
        }
        return $articles;
    }
     /**
     * Retrieve selected articles
     * @access protected
     * @return array
     * 
     */
    public function getSelectedArticles() {
        $articles = array();
        //used helper here in order not to override the product model
        $selected = Mage::helper('press/product')->getSelectedArticles(Mage::registry('current_product'));
        if (!is_array($selected)){
            $selected = array();
        }
        foreach ($selected as $article) {
            $articles[$article->getId()] = array('position' => $article->getPosition());
        }
        return $articles;
    }
    /**
     * get row url
     * @access public
     * @return string
     * 
     */
    public function getRowUrl($item){
        return '#';
    }
    /**
     * get grid url
     * @access public
     * @return string
     * 
     */
    public function getGridUrl(){
        return $this->getUrl('*/*/articlesGrid', array(
            'id'=>$this->getProduct()->getId()
        ));
    }
    /**
     * get the current product
     * @access public
     * @return Mage_Catalog_Model_Product
     * 
     */
    public function getProduct(){
        return Mage::registry('current_product');
    }
    /**
     * Add filter
     * @access protected
     * @param object $column
     * @return Easylife_Press_Block_Adminhtml_Catalog_Product_Edit_Tab_Article
     * 
     */
    protected function _addColumnFilterToCollection($column){
        if ($column->getId() == 'in_articles') {
            $articleIds = $this->_getSelectedArticles();
            if (empty($articleIds)) {
                $articleIds = 0;
            }
            if ($column->getFilter()->getValue()) {
                $this->getCollection()->addFieldToFilter('entity_id', array('in'=>$articleIds));
            } 
            else {
                if($articleIds) {
                    $this->getCollection()->addFieldToFilter('entity_id', array('nin'=>$articleIds));
                }
            }
        } 
        else {
            parent::_addColumnFilterToCollection($column);
        }
        return $this;
    }
}

And last, a controller to handle the ajax requests for your custom grid.
app/code/local/Easylife/Press/controllers/Adminhtml/Press/Article/Catalog/ProductController.php

<?php
require_once ("Mage/Adminhtml/controllers/Catalog/ProductController.php");
class Easylife_Press_Adminhtml_Press_Article_Catalog_ProductController extends Mage_Adminhtml_Catalog_ProductController{
    /**
     * construct
     * @access protected
     * @return void
     * 
     */
    protected function _construct(){
        // Define module dependent translate
        $this->setUsedModuleName('Easylife_Press');
    }
    /**
     * articles in the catalog page
     * @access public
     * @return void
     * 
     */
    public function articlesAction(){
        $this->_initProduct();
        $this->loadLayout();
        $this->getLayout()->getBlock('product.edit.tab.article')
            ->setProductArticles($this->getRequest()->getPost('product_articles', null));
        $this->renderLayout();
    }
    /**
     * articles grid in the catalog page
     * @access public
     * @return void
     * 
     */
    public function articlesGridAction(){
        $this->_initProduct();
        $this->loadLayout();
        $this->getLayout()->getBlock('product.edit.tab.article')
            ->setProductArticles($this->getRequest()->getPost('product_articles', null));
        $this->renderLayout();
    }
}

Just kidding, that wasn't the last thing. You still need to define the layouts for the controller actions. In one of the admin layout files add this:

<adminhtml_press_article_catalog_product_articles>
    <block type="core/text_list" name="root" output="toHtml">
        <block type="press/adminhtml_catalog_product_edit_tab_article" name="product.edit.tab.article"/>
        <block type="adminhtml/widget_grid_serializer" name="article_grid_serializer">
            <reference name="article_grid_serializer">
                <action method="initSerializerBlock">
                    <grid_block_name>product.edit.tab.article</grid_block_name>
                    <data_callback>getSelectedArticles</data_callback>
                    <hidden_input_name>articles</hidden_input_name>
                    <reload_param_name>product_articles</reload_param_name>
                </action>
                <action method="addColumnInputName">
                    <input_name>position</input_name>
                </action>
            </reference>
        </block>
    </block>
</adminhtml_press_article_catalog_product_articles>
<adminhtml_press_article_catalog_product_articlesgrid>
    <block type="core/text_list" name="root" output="toHtml">
        <block type="press/adminhtml_catalog_product_edit_tab_article" name="product.edit.tab.article"/>
    </block>
</adminhtml_press_article_catalog_product_articlesgrid>

I hope I didn't forget any files. Clear the cache and give it a try.

_{Seams complicated. Well it is. But it can be easy. The code above was auto-generated by the Ultimate Module Creator extension. All you need to do with it is to configure the fields of your entity and say that you want a many to may relation with the products. I hope this is not considered self promotion, because the extension is free, you can get it directly from Magento connect, and it really solves this kind of problems.}

I used core_block_abstract_prepare_layout_after event and the observer was as follows:

public function vendorLayout($evt){ // for removing unallowed tabs and buttons from product information edit page.
        $tabBlock = $evt->getEvent()->getBlock();
        if ($tabBlock instanceof Mage_Adminhtml_Block_Catalog_Product_Edit_Tabs) {
            $tab_ids = $tabBlock->getTabsIds();
            $tabs_to_show = array('inventory');
            foreach ($tab_ids as $tab){
                if(!in_array($tab, $tabs_to_show)){
                    $tabBlock->removeTab($tab);
                }
                else{
                    $tabBlock->setActiveTab($tab);
                }
            }
        }
        elseif($tabBlock instanceof Mage_Adminhtml_Block_Catalog_Product_Edit){
            $buttonsToBeRemoved = array('back_button', 'reset_button', 'delete_button', 'duplicate_button', 'save_and_edit_button');
            foreach($buttonsToBeRemoved as $button){
                $tabBlock->unsetChild($button);
            }
        }
    }

first condition removes all the tabs but "inventory", second condition removes all buttons but "save".

Thanks to @mpaepper and @Alex.