Join eav attributes

Question

Im trying to join attributes in my collection on my grid view of "supply needs" from my ERP (Erp boost my shop)

The collection is loaded like this:

$collection = Mage::getModel('Purchase/SupplyNeeds')->getCollection();

And then i tried to join it with catalog/product on product_id, which works fine, but it doesnt give me the attribute "product_class" that i want, because it tries to load it from purchase/supplyneeds.

I have joined it like this:

$collection->join('catalog/product', 'product_id=entity_id');

Which gives me a collection that looks like this for each product:

[product_id] => 8728
[manufacturer_id] => 570
[sku] => 18369
[name] => NEW - Tiny Teasers Opladelig Bullet Vibrator
[waiting_for_delivery_qty] => 0
[status] => 3_prefered_stock_level
[qty_min] => 0.0000
[qty_max] => 1.0000
[entity_id] => 8728
[entity_type_id] => 4
[attribute_set_id] => 17
[type_id] => simple
[has_options] => 0
[required_options] => 0
[created_at] => 2017-08-22 14:01:37
[updated_at] => 2017-08-22 14:04:17
[exclude_from_supply_needs] => 0

But how do i get my attribute product_class in my collection? a foreach takes too much time to load for 600 products

The getSQL looks like this with join statement:

SELECT `main_table`.*, `catalog/product`.* FROM `erp_view_supplyneeds_global` AS `main_table`
 INNER JOIN `catalog_product_entity` AS `catalog/product` ON product_id=entity_id

Answer 1

create main collection of product and join your table with it

 $collection =  Mage::getModel('catalog/product')->getCollection();
 $collection->join('Purchase/SupplyNeeds', 'product_id=entity_id');
 $collection->addAttributeToFilter("product_class",array('neq'=>''));

Or try Below code

 $connection = Mage::getSingleton('core/resource');

 $coll = Mage::getModel('catalog/product')->getCollection()
                 ->addAttributeToFilter('product_class',array('neq'=>''));
 $coll->getSelect()->join( array('supplyNeeds'=> $connection->getTableName('Purchase/SupplyNeeds')), 'supplyNeeds.product_id = e.entity_id', array('supplyNeeds.*' ) ); // here in last parameter pass all fields that you need from your table

Try above code and let me know