Aggregation builder

Creating an Aggregation Builder

You can create a new Aggregation\Builder object with the DocumentManager::createAggregationBuilder() method:

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<?php

$builder = $dm->createAggregationBuilder(\Documents\User::class);
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The first argument indicates the document for which you want to create the builder.

Adding pipeline stages

To add a pipeline stage to the builder, call the corresponding method on the builder object:

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<?php

$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->match()
        ->field('purchaseDate')
        ->gte($from)
        ->lt($to)
        ->field('user')
        ->references($user)
    ->group()
        ->field('id')
        ->expression('$user')
        ->field('numPurchases')
        ->sum(1)
        ->field('amount')
        ->sum('$amount');
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Just like the query builder, the aggregation builder takes care of converting DateTime objects into MongoDB\Driver\BSON\UTCDateTime objects.

Nesting expressions

You can create more complex aggregation stages by using the expr() method in the aggregation builder.

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<?php

$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->match()
        ->field('purchaseDate')
        ->gte($from)
        ->lt($to)
        ->field('user')
        ->references($user)
    ->group()
        ->field('id')
        ->expression(
            $builder->expr()
                ->field('month')
                ->month('$purchaseDate')
                ->field('year')
                ->year('$purchaseDate')
        )
        ->field('numPurchases')
        ->sum(1)
        ->field('amount')
        ->sum('$amount');
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This aggregation would group all purchases by their month and year by projecting those values into an embedded object for the id field. For example:

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{
    _id: {
        month: 1,
        year: 2016
    },
    numPurchases: 1,
    amount: 27.89
}
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Executing an aggregation pipeline

When you are done building your pipeline, you can build an Aggregation object using the getAggregation() method. The returning instance can yield a single result or return an iterator containing all results.

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<?php

$builder = $dm->createAggregationBuilder(\Documents\User::class);
$result = $builder->getAggregation();
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If you instead want to look at the built aggregation pipeline, call the Builder::getPipeline() method.

Hydration

By default, aggregation results are returned as PHP arrays. This is because the result of an aggregation pipeline may look completely different from the source document. In order to get hydrated aggregation results, you first have to map a QueryResultDocument. These are written like regular mapped documents, but they can't be persisted to the database.

Once you have mapped the document, use the hydrate() method to tell the aggregation builder about this document:

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<?php

$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->hydrate(\Documents\UserPurchases::class)
    ->match()
        ->field('purchaseDate')
        ->gte($from)
        ->lt($to)
        ->field('user')
        ->references($user)
    ->group()
        ->field('id')
        ->expression('$user')
        ->field('numPurchases')
        ->sum(1)
        ->field('amount')
        ->sum('$amount');
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When you run the queries, all results will be returned as instances of the specified document.

Disabling Result Caching

Due to MongoDB cursors not being rewindable, ODM uses a caching iterator when returning results from aggregation pipelines. This cache allows you to iterate a result cursor multiple times without re-executing the original aggregation pipeline. However, in long-running processes or when handling a large number of results, this can lead to high memory usage. To disable this result cache, you can tell the query builder to not return a caching iterator:

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<?php

$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder->rewindable(false);
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When setting this option to false, attempting a second iteration will result in an exception. Note that calling getAggregation() will always yield a fresh aggregation instance that can be re-executed.