Magento 1.8 – Get Related Products in Custom Module Admin Grid

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.}

The normal behaviour for the grid checkbox is to bind a js event to it, and action the checkbox check/uncheck. Normally this would be to populate a hidden field with the selected values, and then that field is what gets posted to your controller action.

See varienGrid.prototype /js/mage/adminhtml/grid.js : (this.checkboxCheckCallback) and also setCheckboxChecked method in that class.

For this reason the checkbox element generally do not get a name assigned to it, which you can see if you view your element properties.

This is thus the reason why you cannot get the selected options in your post action, since elements with no name will not post in the form, and you most likely do not have the required callback set to deal with the check/uncheck of the box. Using the callback js, you could also effect other actions in your gui, to enhance the user experience.

However, looking at your usage requirements, you may just get away with setting a name for the checkbox element, which will then post the data to your action.

Thus if you adjust your element definition to this (adding in the 'field_name' property), you will get your data in an array called 'selectedproducts'

$this->addColumn('in_category', array(
                'header_css_class' => 'a-center',
                'type'      => 'checkbox',
                'values'    => $this->_getSelectedProducts(),
                'align'     => 'center',
                'index'     => 'entity_id',
        'name'      => 'in_category',
                'field_name' => 'selectedproducts[]'
            ));

Hope that helps.