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- MongoDB\Collection::watch()
MongoDB\Collection::watch()
New in version 1.3.
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Definition
-
MongoDB\Collection::watch
Executes a change stream operation on the collection. The change stream can be watched for collection-level changes.
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 batch size for the cursor, which will apply to both the initial
aggregate
command and any subsequentgetMore
commands. This determines the maximum number of change events to return in each response from the server.Note
Irrespective of the
batchSize
option, the initialaggregate
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
).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.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 1.13.
fullDocument
string Optional. 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
Note
This is an option of the
$changeStream
pipeline stage.fullDocumentBeforeChange
string Optional. 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
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 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.
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
startAfter
and/orstartAtOperationTime
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. showExpandedEvents
boolean Optional. 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.
Note
This is an option of the
$changeStream
pipeline stage.New in version 1.13.
startAfter
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. UnlikeresumeAfter
, this option can be used with a resume token from an “invalidate” event.Using this option in conjunction with
resumeAfter
and/orstartAtOperationTime
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.
Note
This is an option of the
$changeStream
pipeline stage.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, theoperationTime
returned by the initialaggregate
command will be used if available.Using this option in conjunction with
resumeAfter
and/orstartAfter
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.New in version 1.4.
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.
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.
Assuming that a document was inserted, updated, and deleted while the above script was iterating the change stream, the output would then resemble:
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