Pagination Links

Hey Chuck!

Thank you!

Great question! HATEOS bundle is really cool! But we don't want to show this topic in basics and kept it for the next episode (Symfony REST 5) which was already released a few weeks ago. You can check it http://knpuniversity.com/sc... .

Cheers!

Hi,

thanks for the quick answer.
I just saw that when I take a quick look to the rest of the course.

Any way, great job.

Hey Vlad!

Hmm, interesting! I don't have experience doing this, but in theory, I would be surprised if it's not supported. The error specifically is coming from Doctrine (not the paginator library itself), so changing libraries (probably) won't help.

Could you post your query? By looking at the code in Doctrine near where that error is thrown, it looks like it might be complaining that there is no "root alias" in the query, which means it may just be the query itself that's causing the problems. If you haven't tried it yet, try including the primary key (e.g. alias.id) in the results.

Btw - link to the code in Doctrine fwiw - it's complex, but might help :) https://github.com/doctrine...

Cheers!

Hi Ryan,
I just got it to work! Turns out I had to disable output walkers.

I changed the following line in PaginationFactory::createCollection()

new DoctrineORMAdapter($queryBuilder);```

to

new DoctrineORMAdapter($queryBuilder, true, false);`

thus setting the <strong>$useOutputWalkers</strong> parameter to <strong>false</strong>.

My query is a DTO query with the <strong>NEW</strong> operator, with 5 joins.

What are output walkers anyway, and in which cases are they needed?
Thank you for your hints.

Wow, nice work!

So, output walkers are really advanced. An output walker - which is a less common thing to worry about, there are also tree walkers, which modify the AST - is responsible for turning the "DQL" (represented by an abstract syntax tree - AST) into the actual SQL. In essence, this the actual code that turns the AST into the actual query string. Here's the default walker: https://github.com/doctrine...

In the pagination library, they use a sub-class of this walker: https://github.com/doctrine... - which helps to "count" the query result, used for pagination. That's what you turned off. I'm honestly not sure what the result of that is - but if it works, do it :). Pagination is quite "magical" - since Doctrine needs to take your query and dynamically change it so that it can first get a COUNT of those potential results (without actually fetching all of them). The only thing I'd double-check is that the pagination library is not now querying for ALL the rows, just to get a count of them. Double-check that in the profiler.

Cheers!

Hi Ryan,

I was also able to accomplish this by using a custom ORM adapter that implements <strong>AdapterInterface</strong> and the 2 interface methods. Its constructor has two parameters: a query to get the collection of items and a query to get the total number of items.

Here is the code:

use Doctrine\ORM\QueryBuilder;
use Pagerfanta\Adapter\AdapterInterface;

/**
 * Class CustomORMAdapter
 * @package AppBundle\Pagination
 */
class CustomORMAdapter implements AdapterInterface
{
    /**
     * @var QueryBuilder
     */
    private $queryBuilder;

    /**
     * @var QueryBuilder
     */
    private $countQueryBuilder;

    /**
     * Custom ORM Adapter constructor.
     *
     * @param QueryBuilder $queryBuilder Query builder for the query that returns the collection of items
     * @param QueryBuilder $countQueryBuilder Query builder for the query that returns total number of items
     */
    public function __construct(QueryBuilder $queryBuilder, QueryBuilder $countQueryBuilder)
    {
        $this->queryBuilder = $queryBuilder;
        $this->countQueryBuilder = $countQueryBuilder;
    }

    /**
     * Returns the number of results.
     *
     * @return integer The number of results.
     * @throws \Doctrine\ORM\NonUniqueResultException
     * @throws \Doctrine\ORM\NoResultException
     */
    public function getNbResults()
    {
        return $this->countQueryBuilder
            ->setMaxResults(1)
            ->getQuery()
            ->getSingleScalarResult();
    }

    /**
     * Returns an slice of the results.
     *
     * @param integer $offset The offset.
     * @param integer $length The length.
     *
     * @return array|\Traversable The slice.
     */
    public function getSlice($offset, $length)
    {
        return $this->queryBuilder
            ->setMaxResults($length)
            ->setFirstResult($offset)
            ->getQuery()
            ->getResult();
    }
}

Wow, very clean. I really appreciate you posting your complete solutions inside here - it will definitely help others :)

Thanks!

Thank you, Ryan!