MongoDB\Collection::watch()

Definition

MongoDB\Collection::watch()

Executes a change stream operation on the collection. The change stream can be watched for collection-level changes.

function watch(
    array $pipeline = [],
    array $options = []
): MongoDB\ChangeStream

Parameters

$pipeline : array|object

The pipeline of stages to append to an initial $changeStream stage.

$options : array

An array specifying the desired options.

Name	Type	Description
batchSize	integer	The maximum number of documents within each batch returned in a change stream, which applies to the aggregate command. By default, the aggregate command has an initial batch size of 101 documents and a maximum size of 16 mebibytes (MiB) for each subsequent batch. This option can enforce a smaller limit than 16 MiB, but not a larger one. If you set batchSize to a limit that results in batches larger than 16 MiB, this option has no effect. Irrespective of the batchSize option, the initial aggregate command response for a change stream generally does not include any documents unless another option is used to configure its starting point (e.g. startAfter).
codec	MongoDB\Codec\DocumentCodec	The codec to use for encoding or decoding documents. This option is mutually exclusive with the typeMap option. Defaults to the collection's codec. Inheritance for a default codec option takes precedence over that of the typeMap option. New in version 1.17.
collation	array|object	Collation allows users to specify language-specific rules for string comparison, such as rules for lettercase and accent marks. When specifying collation, the locale field is mandatory; all other collation fields are optional. For descriptions of the fields, see Collation Document. Starting in MongoDB 4.2, defaults to simple binary comparison if omitted. In earlier versions, change streams opened on a single collection would inherit the collection's default collation.
comment	mixed	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 since MongoDB 4.4. Earlier server versions only support string values. New in version 1.13.
fullDocument	string	Determines how the fullDocument response field will be populated for update operations. By default, change streams only return the delta of fields (via an updateDescription field) for update operations and fullDocument is omitted. Insert and replace operations always include the fullDocument field. Delete operations omit the field as the document no longer exists. Specify "updateLookup" to return the current majority-committed version of the updated document. MongoDB 6.0+ allows returning the post-image of the modified document if the collection has changeStreamPreAndPostImages enabled. Specify "whenAvailable" to return the post-image if available or a null value if not. Specify "required" to return the post-image if available or raise an error if not. The following values are supported: MongoDB\Operation\Watch::FULL_DOCUMENT_UPDATE_LOOKUP MongoDB\Operation\Watch::FULL_DOCUMENT_WHEN_AVAILABLE MongoDB\Operation\Watch::FULL_DOCUMENT_REQUIRED This is an option of the $changeStream pipeline stage.
fullDocumentBeforeChange	string	Determines how the fullDocumentBeforeChange response field will be populated. By default, the field is omitted. MongoDB 6.0+ allows returning the pre-image of the modified document if the collection has changeStreamPreAndPostImages enabled. Specify "whenAvailable" to return the pre-image if available or a null value if not. Specify "required" to return the pre-image if available or raise an error if not. The following values are supported: MongoDB\Operation\Watch::FULL_DOCUMENT_BEFORE_CHANGE_WHEN_AVAILABLE MongoDB\Operation\Watch::FULL_DOCUMENT_BEFORE_CHANGE_REQUIRED This is an option of the $changeStream pipeline stage. New in version 1.13.
maxAwaitTimeMS	integer	Positive integer denoting the time limit in milliseconds for the server to block a getMore operation if no data is available.
readConcern	MongoDB\Driver\ReadConcern	Read concern to use for the operation. Defaults to the collection's read concern.
readPreference	MongoDB\Driver\ReadPreference	Read preference to use for the operation. Defaults to the collection's read preference. This is used for both the initial change stream aggregation and for server selection during an automatic resume.
resumeAfter	array|object	Specifies the logical starting point for the new change stream. The _id field in documents returned by the change stream may be used here. Using this option in conjunction with startAfter and/or startAtOperationTime will result in a server error. The options are mutually exclusive. This is an option of the $changeStream pipeline stage.
session	MongoDB\Driver\Session	Client session to associate with the operation.
showExpandedEvents	boolean	If true, instructs the server to include additional DDL events in the change stream. The additional events that may be included are: createIndexes dropIndexes modify create shardCollection reshardCollection (server 6.1+) refineCollectionShardKey (server 6.1+) This is not supported for server versions prior to 6.0 and will result in an exception at execution time if used. This is an option of the $changeStream pipeline stage. New in version 1.13.
startAfter	array|object	Specifies the logical starting point for the new change stream. The _id field in documents returned by the change stream may be used here. Unlike resumeAfter, this option can be used with a resume token from an "invalidate" event. Using this option in conjunction with resumeAfter and/or startAtOperationTime will result in a server error. The options are mutually exclusive. This is not supported for server versions prior to 4.2 and will result in an exception at execution time if used. This is an option of the $changeStream pipeline stage. New in version 1.5.
startAtOperationTime	MongoDB\BSON\TimestampInterface	If specified, the change stream will only provide changes that occurred at or after the specified timestamp. Command responses from a MongoDB 4.0+ server include an operationTime that can be used here. By default, the operationTime returned by the initial aggregate command will be used if available. Using this option in conjunction with resumeAfter and/or startAfter will result in a server error. The options are mutually exclusive. This is not supported for server versions prior to 4.0 and will result in an exception at execution time if used. This is an option of the $changeStream pipeline stage.
typeMap	array	The type map to apply to cursors, which determines how BSON documents are converted to PHP values. Defaults to the collection's type map.

Return Values

A MongoDB\ChangeStream object, which allows for iteration of events in the change stream via the Iterator interface.

Errors/Exceptions

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 extension level (e.g. connection errors).

Examples

This example reports events while iterating a change stream.

<?php
$uri = 'mongodb://rs1.example.com,rs2.example.com/?replicaSet=myReplicaSet';
$collection = (new MongoDB\Client($uri))->test->inventory;
$changeStream = $collection->watch();
for ($changeStream->rewind(); true; $changeStream->next()) {
    if ( ! $changeStream->valid()) {
        continue;
    }
    $event = $changeStream->current();
    if ($event['operationType'] === 'invalidate') {
        break;
    }
    $ns = sprintf('%s.%s', $event['ns']['db'], $event['ns']['coll']);
    $id = json_encode($event['documentKey']['_id']);
    switch ($event['operationType']) {
        case 'delete':
            printf("Deleted document in %s with _id: %s\n\n", $ns, $id);
            break;
        case 'insert':
            printf("Inserted new document in %s\n", $ns);
            echo json_encode($event['fullDocument']), "\n\n";
            break;
        case 'replace':
            printf("Replaced new document in %s with _id: %s\n", $ns, $id);
            echo json_encode($event['fullDocument']), "\n\n";
            break;
        case 'update':
            printf("Updated document in %s with _id: %s\n", $ns, $id);
            echo json_encode($event['updateDescription']), "\n\n";
            break;
    }
}

Assuming that a document was inserted, updated, and deleted while the above script was iterating the change stream, the output would then resemble:

Inserted new document in test.user
{"_id":{"$oid":"5b329c4874083047cc05e60a"},"username":"bob"}
Inserted new document in test.products
{"_id":{"$oid":"5b329c4d74083047cc05e60b"},"name":"Widget","quantity":5}
Updated document in test.user with _id: {"$oid":"5b329a4f74083047cc05e603"}
{"updatedFields":{"username":"robert"},"removedFields":[]}

See Also

• MongoDB\Client::watch()

• MongoDB\Database::watch()

• Aggregation Pipeline documentation in the MongoDB Manual

• Change Streams documentation in the MongoDB manual

• Change Events documentation in the MongoDB manual