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MongoDB\Client::watch()

New in version 1.4.

Definition

MongoDB\Client::watch

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

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

This method has the following parameters:

Parameter Type Description
$pipeline array|object Optional. The pipeline of stages to append to an initial $changeStream stage.
$options array Optional. An array specifying the desired options.

The $options parameter supports the following options:

Option Type Description
batchSize integer Optional. Specifies the maximum number of change events to return in each batch of the response from the MongoDB cluster.
collation array|object

Optional. 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.

This option is available in MongoDB 3.4+ and will result in an exception at execution time if specified for an older server version.

fullDocument string

Optional. Allowed values are ‘default’ and ‘updateLookup’. Defaults to ‘default’. When set to ‘updateLookup’, the change notification for partial updates will include both a delta describing the changes to the document, as well as a copy of the entire document that was changed from some time after the change occurred. The following values are supported:

  • MongoDB\Operation\Watch::FULL_DOCUMENT_DEFAULT (default)
  • MongoDB\Operation\Watch::FULL_DOCUMENT_UPDATE_LOOKUP

Note

This is an option of the $changeStream pipeline stage.

maxAwaitTimeMS integer Optional. 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

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

This is used for both the initial change stream aggregation and for server selection during an automatic resume.

resumeAfter array|object

Optional. 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 startAtOperationTime will result in a server error. The options are mutually exclusive.

Note

This is an option of the $changeStream pipeline stage.

session MongoDB\Driver\Session

Optional. Client session to associate with the operation.

Sessions are not supported for server versions prior to 3.6.

startAtOperationTime MongoDB\BSON\TimestampInterface

Optional. 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 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.

Note

This is an option of the $changeStream pipeline stage.

typeMap array Optional. The type map to apply to cursors, which determines how BSON documents are converted to PHP values. Defaults to the client’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 driver 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';

$client = new MongoDB\Client($uri);

$changeStream = $client->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 app.user
{"_id":{"$oid":"5b329b6674083047cc05e607"},"username":"bob"}

Inserted new document in app.products
{"_id":{"$oid":"5b329b6a74083047cc05e608"},"name":"Widget","quantity":5}

Inserted new document in logs.messages
{"_id":{"$oid":"5b329b7374083047cc05e609"},"msg":"bob purchased a widget"}

See Also