Left join order grid collection using observer method. Magento 1.9

Question

I'm trying to add a grid to order listing table following this awesome blog which works if all code copied but I'm unable to customize it. And I want to show the data from my custom table. I've created model, resource model and collection model for my custom table. I have to store the order id from magento file system and order id from payment gateway API in it. My database table looks like this:

Where storeoid is our system's primary key and orderid is the uniques id sent by the payment gateway API.

I have successfully added a grid in order listing table by using event

  <core_layout_block_create_after>
      <observers>
          <magestyapps_ordergrid_add_columns>
              <class>Myname_Mygateway_Model_Observer</class>
              <method>addColumnsToGrid</method>
          </magestyapps_ordergrid_add_columns>
      </observers>
  </core_layout_block_create_after> 

And corresponsing observer for it:

public function addColumnsToGrid(Varien_Event_Observer $observer)
{
    $block = $observer->getEvent()->getBlock();

    // Check whether the loaded block is the orders grid block
    if (!($block instanceof Mage_Adminhtml_Block_Sales_Order_Grid)
        || $block->getNameInLayout() != 'sales_order.grid'
    ) {
        return $this;
    }

    // Add a new column rigth after the "Ship to Name" column
    $block->addColumnAfter('bankoid', [
        'header' => $block->__('Bank Order Id'),
        'index' => 'bankoid',
    ], 'shipping_name');

    return $this;
}

I can see the grid added in backend. Next I'm trying to load the order grid collection with data from my custom table. I listen to this event:

  <sales_order_grid_collection_load_before>
      <observers>
          <magestyapps_ordergrid_prepare_collection>
              <class>Myname_Mygateway_Model_Observer</class>
              <method>prepareOrderGridCollection</method>
          </magestyapps_ordergrid_prepare_collection>
      </observers>
  </sales_order_grid_collection_load_before>

And it's observer is:

public function prepareOrderGridCollection(Varien_Event_Observer $observer)
{
    $collection = $observer->getEvent()->getOrderGridCollection(); // grid collection

         $orderCollection = Mage::getResourceModel('myname_mygateway/createorder');
        $orderCollection->getSelect()
            ->reset(Zend_Db_Select::COLUMNS)
            ->columns(['soid' => 'storeoid', 'orderid']);

         $collection->getSelect()    
             ->joinLeft(['order' => $orderCollection->getSelect()],
                 'order.order_id = main_table.entity_id',
                 ['bankoid']); // just join the grid collection and the another in this case sales/order_coll, I'll have to replace later one.

     return $this;
}

I get error in backend :

Call to a member function getSelect() on null

If I can do joins and show result by directly using table's name then suggest me that as well. So please help me solve my problem.

Answer 1

I solved my problem by making following changes:

public function prepareOrderGridCollection(Varien_Event_Observer $observer)
{
    $collection = $observer->getEvent()->getOrderGridCollection(); // grid collection

$collection->getSelect()->joinLeft(
   'myname_mygateway_createorder', //joining table name
// note this join clause!
   'main_table.increment_id = myname_mygateway_createorder.storeoid',
   array('orderid')
);
var_dump((string)$collection->getSelect());
// die();

return $this;
}

And in the

public function addColumnsToGrid(Varien_Event_Observer $observer)
{
    $block = $observer->getEvent()->getBlock();

    // Check whether the loaded block is the orders grid block
    if (!($block instanceof Mage_Adminhtml_Block_Sales_Order_Grid)
        || $block->getNameInLayout() != 'sales_order.grid'
    ) {
        return $this;
    }

    // Add a new column rigth after the "Ship to Name" column
    $block->addColumnAfter('orderid', [
        'header' => $block->__('Bank Order Id'),
        'index' => 'orderid',
    ], 'shipping_name');

    return $this;
}