Aggregation 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

You can execute a pipeline using the execute() method. This will run the aggregation pipeline and return a cursor for you to iterate over the results:

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<?php

$builder = $dm->createAggregationBuilder(\Documents\User::class);
$result = $builder->execute();
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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.

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<?php

namespace Documents;

/** @QueryResultDocument */
class UserPurchases
{
    /** @ReferenceOne(targetDocument=User::class, name="_id") */
    private $user;

    /** @Field(type="int") */
    private $numPurchases;

    /** @Field(type="float") */
    private $amount;
}
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<?xml version="1.0" encoding="UTF-8"?>
<doctrine-mongo-mapping xmlns="http://doctrine-project.org/schemas/odm/doctrine-mongo-mapping"
                  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                  xsi:schemaLocation="http://doctrine-project.org/schemas/odm/doctrine-mongo-mapping
                  http://doctrine-project.org/schemas/odm/doctrine-mongo-mapping.xsd">
    <query-result-document name="Documents\UserPurchases">
        <field field-name="numPurchases" type="int" />
        <field field-name="amount" type="float" />
        <reference-one field="user" target-document="Documents\User" name="_id" />
    </query-result-document>
</doctrine-mongo-mapping>
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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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$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder->setRewindable(false);
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When setting this option to false, attempting a second iteration will result in an exception.

$addFields

Adds new fields to documents. $addFields outputs documents that contain all existing fields from the input documents and newly added fields.

The $addFields stage is equivalent to a $project stage that explicitly specifies all existing fields in the input documents and adds the new fields.

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<?php

$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->addFields()
        ->field('purchaseYear')
        ->year('$purchaseDate');
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You can also pass expressions as arrays:

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$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->addFields()
        ->field('purchaseYear')
        ->expression(['$year' => '$purchaseDate'])
        ->field('multiply')
        ->expression(['$multiply' => ['$price', 2 ] ]);
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This allows usage of any expression operators introduced by MongoDB, even if Doctrine ODM does not yet wrap it with convenience methods.

You can see all available expression operators at MongoDB documentation here.

$bucket

Categorizes incoming documents into groups, called buckets, based on a specified expression and bucket boundaries.

Each bucket is represented as a document in the output. The document for each bucket contains an _id field, whose value specifies the inclusive lower bound of the bucket and a count field that contains the number of documents in the bucket. The count field is included by default when the output is not specified.

$bucket only produces output documents for buckets that contain at least one input document.

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$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->bucket()
        ->groupBy('$itemCount')
        ->boundaries(1, 2, 3, 4, 5, '5+')
        ->defaultBucket('5+')
        ->output()
            ->field('lowestValue')
            ->min('$value')
            ->field('highestValue')
            ->max('$value')
;
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$bucketAuto

Similar to $bucket, except that boundaries are automatically determined in an attempt to evenly distribute the documents into the specified number of buckets.

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$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->bucketAuto()
        ->groupBy('$itemCount')
        ->buckets(5)
        ->output()
            ->field('lowestValue')
            ->min('$value')
            ->field('highestValue')
            ->max('$value')
;
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$collStats

The $collStats stage returns statistics regarding a collection or view.

$count

Returns a document that contains a count of the number of documents input to the stage.

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<?php

$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->match()
        ->field('itemCount')
        ->eq(1)
    ->count('numSingleItemOrders')
;
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The example above returns a single document with the numSingleItemOrders containing the number of orders found.

$facet

Processes multiple aggregation pipelines within a single stage on the same set of input documents. Each sub-pipeline has its own field in the output document where its results are stored as an array of documents.

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<?php

$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->facet()
        ->field('groupedByItemCount')
        ->pipeline(
            $dm->createAggregationBuilder(\Documents\Orders::class)->group()
                ->field('id')
                ->expression('$itemCount')
                ->field('lowestValue')
                ->min('$value')
                ->field('highestValue')
                ->max('$value')
                ->field('totalValue')
                ->sum('$value')
                ->field('averageValue')
                ->avg('$value')
        )
        ->field('groupedByYear')
        ->pipeline(
            $dm->createAggregationBuilder(\Documents\Orders::class)->group()
                ->field('id')
                ->year('purchaseDate')
                ->field('lowestValue')
                ->min('$value')
                ->field('highestValue')
                ->max('$value')
                ->field('totalValue')
                ->sum('$value')
                ->field('averageValue')
                ->avg('$value')
        )
;
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$geoNear

The $geoNear stage finds and outputs documents in order of nearest to farthest from a specified point.

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$builder = $this->dm->createAggregationBuilder(\Documents\City::class);
$builder
    ->geoNear(120, 40)
    ->spherical(true)
    ->distanceField('distance')
    // Convert radians to kilometers (use 3963.192 for miles)
    ->distanceMultiplier(6378.137);
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$graphLookup

Performs a recursive search on a collection, with options for restricting the search by recursion depth and query filter. The $graphLookup stage can be used to resolve association graphs and flatten them into a single list.

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$builder = $this->dm->createAggregationBuilder(\Documents\Traveller::class);
$builder
    ->graphLookup('nearestAirport')
        ->connectFromField('connections')
        ->maxDepth(2)
        ->depthField('numConnections')
        ->alias('destinations');
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$group

The $group stage is used to do calculations based on previously matched documents:

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<?php

$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->match()
        ->field('user')
        ->references($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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$indexStats

The $indexStats stage returns statistics regarding the use of each index for the collection. More information can be found in the official Documentation

$lookup

The $lookup stage is used to fetch documents from different collections in pipeline stages. Take the following relationship for example:

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/**
 * @ReferenceMany(
 *     targetDocument=Documents\Item::class,
 *     cascade="all",
 *     storeAs="id"
 * )
 */
private $items;
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$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->lookup('items')
        ->alias('items');
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In MongoDB 3.2, the resulting array will be empty for a one-to-many relationship, you need to unwind your field at first and use a group stage afterwards.

The resulting array will contain all matched item documents in an array. This has to be considered when looking up one-to-one relationships:

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/**
 * @ReferenceOne(
 *     targetDocument=Documents\Item::class,
 *     cascade="all",
 *     storeAs="id"
 * )
 */
private $items;
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$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->lookup('user')
        ->alias('user')
    ->unwind('$user');
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MongoDB will always return an array, even if the lookup only returned a single document. Thus, when looking up one-to-one references the result must be flattened using the $unwind operator.

Looking up a reference nested in an embedded document (like ->lookup('embedDoc.refDocs')) is not supported. You'll need to make your lookup as if your Reference was not mapped See below for more.

You can also configure your lookup manually if you don't have it mapped in your document:

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$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->lookup('unmappedCollection')
        ->localField('_id')
        ->foreignField('userId')
        ->alias('items');
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$match

The $match stage lets you filter documents according to certain criteria. It works just like the query builder:

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<?php

$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->match()
        ->field('purchaseDate')
        ->gte($from)
        ->lt($to)
        ->field('user')
        ->references($user);
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You can also use fields defined in previous stages:

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$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->project()
        ->excludeFields(['_id'])
        ->includeFields(['purchaseDate', 'user'])
        ->field('purchaseYear')
        ->year('$purchaseDate')
    ->match()
        ->field('purchaseYear')
        ->equals(2016);
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$out

The $out stage is used to store the result of the aggregation pipeline in a collection instead of returning an iterable cursor of results. This must be the last stage in an aggregation pipeline.

If the collection specified by the $out operation already exists, then upon completion of the aggregation, the existing collection is atomically replaced. Any indexes that existed on the collection are left intact. If the aggregation fails, the $out operation does not remove the data from an existing collection.

$project

The $project stage lets you reshape the current document or define a completely new one:

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$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->project()
        ->excludeFields(['_id'])
        ->includeFields(['purchaseDate', 'user'])
        ->field('purchaseYear')
        ->year('$purchaseDate');
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$redact

The redact stage can be used to restrict the contents of the documents based on information stored in the documents themselves. You can read more about the $redact stage in the MongoDB documentation.

The following example taken from the official documentation checks the level field on all document levels and evaluates it to grant or deny access:

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{
    _id: 1,
    level: 1,
    acct_id: "xyz123",
    cc: {
        level: 5,
        type: "yy",
        num: 000000000000,
        exp_date: ISODate("2015-11-01T00:00:00.000Z"),
        billing_addr: {
            level: 5,
            addr1: "123 ABC Street",
            city: "Some City"
        },
        shipping_addr: [
            {
                level: 3,
                addr1: "987 XYZ Ave",
                city: "Some City"
            },
            {
                level: 3,
                addr1: "PO Box 0123",
                city: "Some City"
            }
        ]
    },
    status: "A"
}
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$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->redact()
        ->cond(
            $builder->expr()->gte('$$level', 5),
            '$$PRUNE',
            '$$DESCEND'
        )
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$replaceRoot

Promotes a specified document to the top level and replaces all other fields. The operation replaces all existing fields in the input document, including the _id field. You can promote an existing embedded document to the top level, or create a new document for promotion.

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$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->replaceRoot('$embeddedField');

$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->replaceRoot()
        ->field('averagePricePerItem')
        ->divide('$value', '$itemCount');
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$sample

The sample stage can be used to randomly select a subset of documents in the aggregation pipeline. It behaves like the $limit stage, but instead of returning the first n documents it returns n random documents.

$sort, $limit and $skip

The $sort, $limit and $skip stages behave like the corresponding query options, allowing you to control the order and subset of results returned by the aggregation pipeline.

$sortByCount

Groups incoming documents based on the value of a specified expression, then computes the count of documents in each distinct group.

Each output document contains two fields: an _id field containing the distinct grouping value, and a count field containing the number of documents belonging to that grouping or category.

The documents are sorted by count in descending order.

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$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder->sortByCount('$items');
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The example above is equivalent to the following pipeline:

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$builder = $dm->createAggregationBuilder(\Documents\Orders::class);
$builder
    ->group()
        ->field('_id')
        ->expression('$items')
        ->field('count')
        ->sum(1)
    ->sort(['count' => -1])
;
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$unwind

The $unwind stage flattens an array in a document, returning a copy for each item. Take this sample document:

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{
    _id: {
        month: 1,
        year: 2016
    },
    purchaseDates: [
        '2016-01-07',
        '2016-03-10',
        '2016-06-25'
    ]
}
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To flatten the purchaseDates array, we would apply the following pipeline stage:

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$builder = $dm->createAggregationBuilder(\Documents\User::class);
$builder->unwind('$purchaseDates');
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The stage would return three documents, each containing a single purchase date:

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{
    _id: {
        month: 1,
        year: 2016
    },
    purchaseDates: '2016-01-07'
},
{
    _id: {
        month: 1,
        year: 2016
    },
    purchaseDates: '2016-03-10'
},
{
    _id: {
        month: 1,
        year: 2016
    },
    purchaseDates: '2016-06-25'
}
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