drop Event事件

A BSON object which serves as an identifier for the change stream event. This value is used as the resumeToken for the resumeAfter parameter when resuming a change stream. The _id object has the following form:BSON对象，用作更改流事件的标识符。在恢复更改流时，此值用作resumeAfter参数的resumeToken。_id对象具有以下形式：

{
   "_data" : <BinData|hex string>
}

The _data type depends on the MongoDB versions and, in some cases, the feature compatibility version (FCV) at the time of the change stream's opening or resumption. _data类型取决于MongoDB版本，在某些情况下，还取决于更改流打开或恢复时的功能兼容性版本（FCV）。See Resume Tokens for the full list of _data types.有关_data类型的完整列表，请参阅恢复令牌。

For an example of resuming a change stream by resumeToken, see Resume a Change Stream.有关通过resumeToken恢复更改流的示例，请参阅恢复更改流。

clusterTime is the timestamp from the oplog entry associated with the event.是与事件关联的oplog条目的时间戳。

Due to oplog size limits, multi-document transactions may create multiple oplog entries. 由于oplog大小的限制，多文档事务可能会创建多个oplog条目。In a transaction, change stream events staged in a given oplog entry share the same clusterTime.在事务中，给定oplog条目的变更流事件共享相同的clusterTime。

Events with the same clusterTime may not all relate to the same transaction. 具有相同clusterTime的事件可能并不都与同一事务相关。Some events don't relate to a transaction at all. Starting in MongoDB 8.0, this may be true for events on any deployment. In previous versions, this behavior was possible only for events on a sharded cluster.有些事件根本与事务无关。从MongoDB 8.0开始，这可能适用于任何部署上的事件。在以前的版本中，这种行为仅适用于分片集群上的事件。

To identify events for a single transaction, you can use the combination of lsid and txnNumber in the change stream event document.要识别单个事务的事件，可以在更改流事件文档中使用lsid和txnNumber的组合。

If the change occurred on a collection, collectionUUID indicates the collection's UUID. If the change occurred on a view, collectionUUID doesn't exist.如果更改发生在集合上，则collectionUUID表示集合的UUID。如果更改发生在视图上，则collectionUUID不存在。

The identifier for the session associated with the transaction.与事务关联的会话的标识符。

Only present if the operation is part of a multi-document transaction.仅当操作是多文档事务的一部分时才存在。

The namespace (database and or collection) affected by the event.受事件影响的命名空间（数据库和/或集合）。

The name of the collection where the event occurred.发生事件的集合的名称。

The name of the database where the event occurred.发生事件的数据库的名称。

The type of operation that the change notification reports.更改通知报告的操作类型。

Returns a value of drop for these change events.返回这些更改事件的drop值。

Together with the lsid, a number that helps uniquely identify a transction.与lsid一起，一个有助于唯一标识事务的数字。

Only present if the operation is part of a multi-document transaction.仅当操作是多文档事务的一部分时才存在。

The server date and time of the database operation. wallTime differs from clusterTime in that clusterTime is a timestamp taken from the oplog entry associated with the database operation event.数据库操作的服务器日期和时间。wallTime与clusterTime的不同之处在于，clusterTime是从与数据库操作事件关联的oplog条目中获取的时间戳。