For unsharded collections this contains a single field _id. 对于未共享的集合，它包含一个字段_id。For sharded collections, this will contain all the components of the shard key对于分片集合，它将包含分片键的所有组件
_id
Generated using TypeDoc
For unsharded collections this contains a single field对于未共享的集合，它包含一个字段_id._id。For sharded collections, this will contain all the components of the shard key对于分片集合，它将包含分片键的所有组件