- Change Streams >
- Change Events
Change Events¶
Change Events¶
The following document represents all possible fields that a change stream response document can have.
Some fields are only available for certain operations, such as updates. The following table describes each field in the change stream response document:
Field | Type | Description |
---|---|---|
_id |
document | Metadata related to the operation. Use this document as a |
operationType |
string | The type of operation that occurred. Can be any of the following values:
|
fullDocument |
document | The document created or modified by the operation. For For For |
ns |
document | The namespace of the database and collection the change stream is open against. |
ns.db |
string | The name of the database. |
ns.coll |
string | The name of the collection. |
documentKey |
document | The document that contains the _id of the document created or modified by the operation.
For sharded collections, also displays the full shard key for the
document. The _id field is not repeated if it is already a
part of the shard key. |
updateDescription |
document | A document describing the fields that were updated or removed by the update operation. This document and its fields only appears if the |
updateDescription.updatedFields |
document | A document whose keys correspond to the fields that were modified by the update operation. The value of each field corresponds to the new value of those fields, rather than the operation that resulted in the new value. |
updateDescription.removedFields |
array | An array of fields that were removed by the update operation. |
insert
Event¶
The following example illustrates an insert
event:
The documentKey
field includes both the _id
and the userName
field. This indicates that the engineering.users
collection is sharded,
with a shard key on userName
and _id
.
The fullDocument
document represents the version of the document at the
time of the insert.
update
Event¶
The following example illustrates an update
event:
The following example illustrates an update
event for change streams
opened with the fullDocument : updateLookup
option:
The fullDocument
document represents the most current majority-committed
version of the updated document. The fullDocument
document may vary from
the document at the time of the update operation depending on the number of
interleaving majority-committed operations that occur between the update
operation and the document lookup.
replace
Event¶
The following example illustrates a replace
event:
A replace
operation uses the update command, and consists of two stages:
- Delete the original document with the
documentKey
and - Insert the new document using the same
documentkey
The fullDocument
of a replace
event represents the document after the
insert of the replacement document.
delete
Event¶
The following example illustrates a delete
event:
The fullDocument
document is omitted as the document no longer exists at the
time the change stream cursor sends the delete
event to the client.
invalidate
Event¶
The following example illustrates an invalidate
event:
For change stream opened against a collection,
invalidate
events occur after a dropDatabase
,
drop
, or renameCollection
command that
affects the watched collection. invalidate
events close the change
stream cursor and signal that any locally cached data is out
of sync with the server.
invalidate
events close the change stream cursor.
You cannot resume a change stream after an invalidate event (for example, a collection drop or rename) closes the stream.