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New in version 1.5.



Runs a specified admin/diagnostic pipeline which does not require an underlying collection. For aggregations on collection data, see MongoDB\Collection::aggregate().

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. The default is false.
batchSize integer Optional. Specifies the initial batch size for the cursor. A batchSize of 0 means an empty first batch and is useful for quickly returning a cursor or failure message without doing significant server-side work.
bypassDocumentValidation boolean

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

This option is available in MongoDB 3.2+ and is ignored for older server versions, which do not support document level validation.

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

Document validation requires MongoDB 3.2 or later: if you are using an earlier version of MongoDB, this option will be ignored.

comment string Optional. Users can specify an arbitrary string to help trace the operation through the database profiler, currentOp, and logs.
explain boolean Optional. Specifies whether or not to return the information on the processing of the pipeline.
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.
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 database’s read concern.

This is not supported for server versions prior to 3.2 and will result in an exception at execution time if used.

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

Optional. Client session to associate with the operation.

Sessions are not supported for server versions prior to 3.6.

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

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

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

This is not supported for server versions prior to 3.4 and will result in an exception at execution time if used.

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).

See Also