Observers

In the previous chapter Subjects , we have discussed when a subject is needed and how it can be implemented.

When do I need an observer?

As a subject itself usually will not implement the main import business logic, this will be the observers' responsibility. So it would help if you implemented an observer when

You want to load data from the database based on values you found in the import file
You want to load data to make it available for the following observers or subjects
You want to persist data assembled from values you found in a row of an import file

In general, you need an observer when you want to do something with a row.

How to implement an observer?

The TechDivision\Import\Observers\AbstractObserver will be a perfect choice to be extended by our first observer implementation. At least an observer has to implement the interface TechDivision\Import\Observers\ObserverInterface.

Our example observer tries to load the product with the SKU found in the actual row and adds the SKU to entity_id mapping to the subject.

namespace TechDivision\Import\Product\Observers;

use TechDivision\Import\Utils\RegistryKeys;
use TechDivision\Import\Subjects\SubjectInterface;
use TechDivision\Import\Observers\AbstractObserver;

class MyObserver extends AbstractObserver
{

    /**
     * The product bunch processor instance.
     *
     * @var \TechDivision\Import\Product\Services\ProductBunchProcessorInterface
     */
    protected $processor;

    /**
     * Initialize the observer with the passed product bunch processor instance.
     *
     * @param \TechDivision\Import\Product\Services\ProductBunchProcessorInterface $productBunchProcessor The product bunch processor instance
     */
    public function __construct(ProductBunchProcessorInterface $processor)
    {
        $this->processor = $processor;
    }

    /**
     * Will be invoked by the subject once for every row.
     *
     * @param \TechDivision\Import\Subjects\SubjectInterface $subject The subject instance
     *
     * @return array The modified row
     * @see \TechDivision\Import\Observers\ObserverInterface::handle()
     */
    public function handle(SubjectInterface $subject)
    {

        // initialize the row
        $this->setSubject($subject);
        $this->setRow($subject->getRow());

        // try to load the product with the SKU of the actual row and store the entity ID => SKU mapping in the subject
        if ($product = $this->processor->loadProduct($this->getValue(ColumnKeys::SKU)) {
            $this->subject->addSkuEntityIdMapping($product[MemberNames::ENTITY_ID], $product[MemberNames::SKU]);
        } else {
            throw new \Exception(sprintf('Can\'t load product with SKU "%s"', $sku));
        }

        // return the processed row
        return $this->getRow();
    }
}