Why are my product results inconsistent?

Question

Synopsis

I have created a Helper class which is used to collect all associated products (Simple) for a Grouped Product. To clarify the purpose of this helper, my intention is once I have the children products I will build a different array to return for my view.

I have discovered an inconsistency with the results. In the Admin I have created a Grouped Product, I associated three Simple products.

Example #1:

$children = $this->getAssociatedProducts();
Zend_Debug::dump( count($children) ); // Output: int(1)

Evidently I am missing two products by this result, coincidentally the only product output is the last associated product in the control panel. However I then queried the database and found conflicting results as expected.

Example #2:

$children = $read->fetchAll($select);
Zend_Debug::dump( count($children) ); // Output: int(3)

Furthermore I continued to run through the Magento Core line by line to understand the underlying functionality, as usual I found nothing more than over-complicated processing.

I was hoping someone could enlighten me about how getAssociatedProducts works, more so to understand why I don't receive all of my expected results.

Snippet/Examples

File: app/code/local/Myvendor/MyModule/Helper/View/Product/Grid.php

<?php

class Myvendor_Mymodule_Helper_View_Product_Grid extends Mage_Core_Helper_Abstract
{
    public function getProducts(Mage_Catalog_Model_Product $product)
    {
        // Get a blank instance of the type model for validation.
        $modelType = $product->getTypeInstance(true);
        if (! $modelType instanceof Mage_Catalog_Model_Product_Type_Grouped) {
            Mage::throwException(sprintf(
                'Argument #1 expects type %s, %s given.', 
                'Mage_Catalog_Model_Product_Type_Grouped',
                get_class($modelType)
            ));
        }

        // XXX - When Magento ORM doesn't work as intended or expected - use Zend query builder!

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

        $tableProducts  = $adapter->getTableName('catalog/product');
        $tableRelations = $adapter->getTableName('catalog/product_relation');
        $read           = $adapter->getConnection('read');

        $select = $read->select()
            ->from(['main_table' => $tableRelations], [
                'product.*',
            ])
            ->joinLeft(['product' => $tableProducts], '(main_table.child_id = product.entity_id)', null)
            ->where('main_table.parent_id = ?', (int) $product->getId());

        $children = $read->fetchAll($select);

        Zend_Debug::dump((string) $select);
        Zend_Debug::dump(count($children));
        die;

        return array();
    }
}

Answer 1

First of all make sure you reindexed everything.

When using getAssociatedProducts the product collection is retrieved this way:

$collection = $this->getAssociatedProductCollection($product)
                ->addAttributeToSelect('*')
                ->addFilterByRequiredOptions()
                ->setPositionOrder()
                ->addStoreFilter($this->getStoreFilter($product))
                ->addAttributeToFilter('status', array('in' => $this->getStatusFilters($product)));

There are some filters in this method.
addFilterByRequiredOptions - make sure the child products don't have custom options (and they are simple or virtual).
addAttributeToFilter - make sure they are enabled

Also make sure the products are in stock or that you have the flag Show out of stock products set to yes.