# `change_stream` – Watch changes on a collection, database, or cluster

Watch changes on a collection, a database, or the entire cluster.

class pymongo.change_stream.ChangeStream(target, pipeline, full_document, resume_after, max_await_time_ms, batch_size, collation, start_at_operation_time, session, start_after, comment=None, full_document_before_change=None, show_expanded_events=None)

  The internal abstract base class for change stream cursors.

  Should not be called directly by application developers. Use `pymongo.collection.Collection.watch()`, `pymongo.database.Database.watch()`, or `pymongo.mongo_client.MongoClient.watch()` instead.

  Added in version 3.6.

  See also

  The MongoDB documentation on changeStreams.

  Parameters:

    - target (Union[MongoClient[_DocumentType], Database[_DocumentType], Collection[_DocumentType]])

    - pipeline (Optional[_Pipeline])

    - full_document (Optional[str])

    - resume_after (Optional[Mapping[str, Any]])

    - max_await_time_ms (Optional[int])

    - batch_size (Optional[int])

    - collation (Optional[_CollationIn])

    - start_at_operation_time (Optional[Timestamp])

    - session (Optional[ClientSession])

    - start_after (Optional[Mapping[str, Any]])

    - comment (Optional[Any])

    - full_document_before_change (Optional[str])

    - show_expanded_events (Optional[bool])

  property alive: bool

    Does this cursor have the potential to return more data?

    Note

    Even if `alive` is `True`, `next()` can raise `StopIteration` and `try_next()` can return `None`.

    Added in version 3.8.

  close()

    Close this ChangeStream.

    Return type:

      None

  next()

    Advance the cursor.

    This method blocks until the next change document is returned or an unrecoverable error is raised. This method is used when iterating over all changes in the cursor. For example:

        try:
            resume_token = None
            pipeline = [{'$match': {'operationType': 'insert'}}]
            with db.collection.watch(pipeline) as stream:
                for insert_change in stream:
                    print(insert_change)
                    resume_token = stream.resume_token
        except pymongo.errors.PyMongoError:
            # The ChangeStream encountered an unrecoverable error or the
            # resume attempt failed to recreate the cursor.
            if resume_token is None:
                # There is no usable resume token because there was a
                # failure during ChangeStream initialization.
                logging.error('...')
            else:
                # Use the interrupted ChangeStream's resume token to create
                # a new ChangeStream. The new stream will continue from the
                # last seen insert change without missing any events.
                with db.collection.watch(
                        pipeline, resume_after=resume_token) as stream:
                    for insert_change in stream:
                        print(insert_change)

    Raises `StopIteration` if this ChangeStream is closed.

    Return type:

      _DocumentType

  property resume_token: Mapping[str, Any] | None

    The cached resume token that will be used to resume after the most recently returned change.

    Added in version 3.9.

  try_next()

    Advance the cursor without blocking indefinitely.

    This method returns the next change document without waiting indefinitely for the next change. For example:

        with db.collection.watch() as stream:
            while stream.alive:
                change = stream.try_next()
                # Note that the ChangeStream's resume token may be updated
                # even when no changes are returned.
                print("Current resume token: %r" % (stream.resume_token,))
                if change is not None:
                    print("Change document: %r" % (change,))
                    continue
                # We end up here when there are no recent changes.
                # Sleep for a while before trying again to avoid flooding
                # the server with getMore requests when no changes are
                # available.
                time.sleep(10)

    If no change document is cached locally then this method runs a single getMore command. If the getMore yields any documents, the next document is returned, otherwise, if the getMore returns no documents (because there have been no changes) then `None` is returned.

    Returns:

      The next change document or `None` when no document is available after running a single getMore or when the cursor is closed.

    Return type:

      _DocumentType | None

    Added in version 3.8.

class pymongo.change_stream.ClusterChangeStream(target, pipeline, full_document, resume_after, max_await_time_ms, batch_size, collation, start_at_operation_time, session, start_after, comment=None, full_document_before_change=None, show_expanded_events=None)

  A change stream that watches changes on all collections in the cluster.

  Should not be called directly by application developers. Use helper method `pymongo.mongo_client.MongoClient.watch()` instead.

  Added in version 3.7.

  Parameters:

    - target (Union[MongoClient[_DocumentType], Database[_DocumentType], Collection[_DocumentType]])

    - pipeline (Optional[_Pipeline])

    - full_document (Optional[str])

    - resume_after (Optional[Mapping[str, Any]])

    - max_await_time_ms (Optional[int])

    - batch_size (Optional[int])

    - collation (Optional[_CollationIn])

    - start_at_operation_time (Optional[Timestamp])

    - session (Optional[ClientSession])

    - start_after (Optional[Mapping[str, Any]])

    - comment (Optional[Any])

    - full_document_before_change (Optional[str])

    - show_expanded_events (Optional[bool])

class pymongo.change_stream.CollectionChangeStream(target, pipeline, full_document, resume_after, max_await_time_ms, batch_size, collation, start_at_operation_time, session, start_after, comment=None, full_document_before_change=None, show_expanded_events=None)

  A change stream that watches changes on a single collection.

  Should not be called directly by application developers. Use helper method `pymongo.collection.Collection.watch()` instead.

  Added in version 3.7.

  Parameters:

    - target (Union[MongoClient[_DocumentType], Database[_DocumentType], Collection[_DocumentType]])

    - pipeline (Optional[_Pipeline])

    - full_document (Optional[str])

    - resume_after (Optional[Mapping[str, Any]])

    - max_await_time_ms (Optional[int])

    - batch_size (Optional[int])

    - collation (Optional[_CollationIn])

    - start_at_operation_time (Optional[Timestamp])

    - session (Optional[ClientSession])

    - start_after (Optional[Mapping[str, Any]])

    - comment (Optional[Any])

    - full_document_before_change (Optional[str])

    - show_expanded_events (Optional[bool])

class pymongo.change_stream.DatabaseChangeStream(target, pipeline, full_document, resume_after, max_await_time_ms, batch_size, collation, start_at_operation_time, session, start_after, comment=None, full_document_before_change=None, show_expanded_events=None)

  A change stream that watches changes on all collections in a database.

  Should not be called directly by application developers. Use helper method `pymongo.database.Database.watch()` instead.

  Added in version 3.7.

  Parameters:

    - target (Union[MongoClient[_DocumentType], Database[_DocumentType], Collection[_DocumentType]])

    - pipeline (Optional[_Pipeline])

    - full_document (Optional[str])

    - resume_after (Optional[Mapping[str, Any]])

    - max_await_time_ms (Optional[int])

    - batch_size (Optional[int])

    - collation (Optional[_CollationIn])

    - start_at_operation_time (Optional[Timestamp])

    - session (Optional[ClientSession])

    - start_after (Optional[Mapping[str, Any]])

    - comment (Optional[Any])

    - full_document_before_change (Optional[str])

    - show_expanded_events (Optional[bool])