Add adapter to support Mongo Aggregation Builder

[webdevilopers]

Currently the DoctrineODMMongoDBAdapter only supports the Query Builder:

• https://github.com/doctrine/mongodb-odm/blob/master/lib/Doctrine/ODM/MongoDB/Query/Builder.php

But there is also the Aggregation Builder:

• https://github.com/doctrine/mongodb-odm/blob/master/lib/Doctrine/ODM/MongoDB/Aggregation/Builder.php

Adding an additional adapter based on the existing one is actually easy:

use Doctrine\ODM\MongoDB\Aggregation\Builder;
use Pagerfanta\Adapter\AdapterInterface;

class DoctrineODMMongoDBAggregationAdapter implements AdapterInterface
{
    private $aggregationBuilder;

    /**
     * Constructor.
     *
     * @param Builder $aggregationBuilder A DoctrineMongo aggregation builder.
     */
    public function __construct(Builder $aggregationBuilder)
    {
        $this->aggregationBuilder = $aggregationBuilder;
    }

    /**
     * Returns the query builder.
     *
     * @return Builder The query builder.
     */
    public function getAggregationBuilder()
    {
        return $this->aggregationBuilder;
    }

    /**
     * {@inheritdoc}
     */
    public function getNbResults()
    {
        return $this->aggregationBuilder->execute()->count();
    }

    /**
     * {@inheritdoc}
     */
    public function getSlice($offset, $length)
    {
        return $this->aggregationBuilder
            ->limit($length)
            ->skip($offset)
            ->execute();
    }
}

Unfortunately none of the two builders implement a common Interface. But there is another reason why using a single adapter for both use cases could be problematic!

The aggregation builder uses a pipeline. Each time a so called "stage" e.g. limit oder sort is added the return value of the assigned variable changes.

$qb = $this
    ->createAggregationBuilder();
    ->sort(['leavingDate' => 1])
    ->limit($query->limit);

dump($qb); // Instance of Limit extends Stage

$qb = $this
    ->createAggregationBuilder();
$qb
    ->sort(['leavingDate' => 1])
    ->limit($query->limit);

dump($qb); // Instance of Builder

As soon as you pass a Stage instance you can not retrieve the original builder:

• https://github.com/doctrine/mongodb/blob/master/lib/Doctrine/MongoDB/Aggregation/Stage.php#L19

Also there are plans for ODM version 2 which may change this behaviour:

• Add UPGRADE document for ODM 2.0 doctrine/mongodb-odm#1856

Maybe @alcaeus or @malarzm could comment on this too? Thanks in advance!

Possibly related issues:

• [pagerfanta] The latest Pagerfanta adapter does not appear to be compatible with the library doctrine/mongodb-odm#1988 (comment) @ychanan

[alcaeus]

The aggregation builder is a bit different from the query builder in terms of how it handles its data. I'm not sure which way I like better, but it seemed sensible to build it like this at the time. Either way, while this will store a reference to a query builder:

$builder = $this->createQueryBuilder()
    ->field('foo')->equals('bar');

this will not store a reference to an aggregation builder, but rather to a single match stage:

$builder = $this->createAggregationBuilder()
    ->match()
         ->field('foo')->equals('bar');

If you want to store the builder object, you definitely want to first create an aggregation builder, then modify it further:

$builder = $this->createAggregationBuilder();
$builder
    ->match()
         ->field('foo')->equals('bar');

Since adding a stage to the builder modifies the builder instance, you'll want to create a clone of $this->aggregationBuilder in your getSlice method, otherwise you'll just end up with multiple conflicting $limit and $skip stages in your pipeline when retrieving multiple pages.

Also there are plans for ODM version 2 which may change this behaviour

Not sure where in that PR you saw that, but right now that sounds like news to me 😉

[malarzm]

Also there are plans for ODM version 2 which may change this behaviour

Not sure where in that PR you saw that, but right now that sounds like news to me ;)

I think this might have been related to doctrine/mongodb-odm#1988 (comment) where the Query' is changing :)