Executes an aggregation framework pipeline operation on the collection.

function aggregate(array $pipeline, array $options = []): Traversable

This method has the following parameters:

Parameter Type Description
$pipeline array Specifies an aggregation pipeline operation.
$options array Optional. An array specifying the desired options.

The $options parameter supports the following options:

Option Type Description
allowDiskUse boolean Optional. Enables writing to temporary files. When set to true, aggregation stages can write data to the _tmp sub-directory in the dbPath directory.
batchSize integer

Optional. Specifies the batch size for the cursor, which will apply to both the initial aggregate command and any subsequent getMore commands. This determines the maximum number of documents to return in each response from the server.

A batchSize of 0 is special in that and will only apply to the initial aggregate command; subsequent getMore commands will use the server’s default batch size. This may be useful for quickly returning a cursor or failure from aggregate without doing significant server-side work.

bypassDocumentValidation boolean

Optional. If true, allows the write operation to circumvent document level validation. Defaults to false.

This only applies when using the $out and $out stages.

comment mixed

Optional. Enables users to specify an arbitrary comment to help trace the operation through the database profiler, currentOp output, and logs.

The comment can be any valid BSON type for server versions 4.4 and above. Earlier server versions only support string values.

New in version 1.3.

explain boolean

Optional. Specifies whether or not to return the information on the processing of the pipeline.

New in version 1.4.

hint string|array|object

Optional. The index to use. Specify either the index name as a string or the index key pattern as a document. If specified, then the query system will only consider plans using the hinted index.

New in version 1.3.

let array|object

Optional. Map of parameter names and values. Values must be constant or closed expressions that do not reference document fields. Parameters can then be accessed as variables in an aggregate expression context (e.g. $$var).

This is not supported for server versions prior to 5.0 and will result in an exception at execution time if used.

New in version 1.9.

maxTimeMS integer Optional. The cumulative time limit in milliseconds for processing operations on the cursor. MongoDB aborts the operation at the earliest following interrupt point.
readConcern MongoDB\Driver\ReadConcern

Optional. Read concern to use for the operation. Defaults to the collection’s read concern.

It is not possible to specify a read concern for individual operations as part of a transaction. Instead, set the readConcern option when starting the transaction with startTransaction.

readPreference MongoDB\Driver\ReadPreference Optional. Read preference to use for the operation. Defaults to the collection’s read preference.
session MongoDB\Driver\Session

Optional. Client session to associate with the operation.

New in version 1.3.

typeMap array Optional. The type map to apply to cursors, which determines how BSON documents are converted to PHP values. Defaults to the collection’s type map.
writeConcern MongoDB\Driver\WriteConcern

Optional. Write concern to use for the operation. Defaults to the collection’s write concern.

It is not possible to specify a write concern for individual operations as part of a transaction. Instead, set the writeConcern option when starting the transaction with startTransaction.

This only applies when a $out or $merge stage is specified.

Return Values

A MongoDB\Driver\Cursor or ArrayIterator object. In both cases, the return value will be Traversable.


MongoDB\Exception\UnexpectedValueException if the command response from the server was malformed.

MongoDB\Exception\UnsupportedException if options are used and not supported by the selected server (e.g. collation, readConcern, writeConcern).

MongoDB\Exception\InvalidArgumentException for errors related to the parsing of parameters or options.

MongoDB\Driver\Exception\RuntimeException for other errors at the driver level (e.g. connection errors).


The following aggregation example uses a collection called names and groups the first_name field together, counts the total number of results in each group, and sorts the results by name.


$collection = (new MongoDB\Client)->test->names;

$cursor = $collection->aggregate(
        ['$group' => ['_id' => '$first_name', 'name_count' => ['$sum' => 1]]],
        ['$sort' => ['_id' => 1]],

See Also