delete Event
Synopsis
delete
A
delete
event occurs when operations remove documents from a collection, such as when a user or application executes thedelete
command.
Description
Field | Type | Description | |||
---|---|---|---|---|---|
_id | Document | A BSON object which serves as an identifier for the
change stream event. This value is used as the
The For an example of resuming a change stream by | |||
clusterTime | Timestamp |
Due to oplog size limits,
multi-document transactions may create multiple
oplog entries. In a transaction, change stream events staged in a given oplog
entry share the same Events with the same To identify events for a single transaction, you can use the
combination of Changed in version 8.0. | |||
collectionUUID | UUID | UUID identifying the collection where the change occurred. New in version 6.0. | |||
documentKey | document | Document that contains the For sharded collections, this field also displays the full shard key
for the document. The | |||
lsid | document | The identifier for the session associated with the transaction. Only present if the operation is part of a multi-document transaction. | |||
ns | document | The namespace (database and or collection) affected by the event. | |||
ns.coll | string | The name of the collection where the event occurred. | |||
ns.db | string | The name of the database where the event occurred. | |||
operationDescription | document | Additional information on the change operation. This document and its subfields only appears when the change stream uses expanded events. New in version 6.0. | |||
operationType | string | The type of operation that the change notification reports. Returns a value of | |||
txnNumber | NumberLong | Together with the lsid, a number that helps uniquely identify a transction. Only present if the operation is part of a multi-document transaction. | |||
wallTime | The server date and time of the database operation. New in version 6.0. |
Behavior
Document Pre- and Post-Images
Starting in MongoDB 6.0, you see a fullDocumentBeforeChange
document with the fields before the document was changed (or deleted)
if you perform these steps:
Enable the new
changeStreamPreAndPostImages
field for a collection usingdb.createCollection()
,create
, orcollMod
.Set
fullDocumentBeforeChange
to"required"
or"whenAvailable"
indb.collection.watch()
.
Example fullDocumentBeforeChange
document in the change stream
output:
"fullDocumentBeforeChange" : { "_id" : ObjectId("599af247bb69cd89961c986d"), "userName" : "alice123", "name" : "Alice Smith" }
For complete examples with the change stream output, see Change Streams with Document Pre- and Post-Images.
Pre- and post-images are not available for a change stream event if the images were:
Not enabled on the collection at the time of a document update or delete operation.
Removed after the pre- and post-image retention time set in
expireAfterSeconds
.The following example sets
expireAfterSeconds
to100
seconds on an entire cluster:use admin db.runCommand( { setClusterParameter: { changeStreamOptions: { preAndPostImages: { expireAfterSeconds: 100 } } } } ) The following example returns the current
changeStreamOptions
settings, includingexpireAfterSeconds
:db.adminCommand( { getClusterParameter: "changeStreamOptions" } ) Setting
expireAfterSeconds
tooff
uses the default retention policy: pre- and post-images are retained until the corresponding change stream events are removed from the oplog.If a change stream event is removed from the oplog, then the corresponding pre- and post-images are also deleted regardless of the
expireAfterSeconds
pre- and post-image retention time.
Additional considerations:
Enabling pre- and post-images consumes storage space and adds processing time. Only enable pre- and post-images if you need them.
Limit the change stream event size to less than 16 megabytes. To limit the event size, you can:
Limit the document size to 8 megabytes. You can request pre- and post-images simultaneously in the change stream output if other change stream event fields like
updateDescription
are not large.Request only post-images in the change stream output for documents up to 16 megabytes if other change stream event fields like
updateDescription
are not large.Request only pre-images in the change stream output for documents up to 16 megabytes if:
document updates affect only a small fraction of the document structure or content, and
do not cause a
replace
change event. Areplace
event always includes the post-image.
To request a pre-image, you set
fullDocumentBeforeChange
torequired
orwhenAvailable
indb.collection.watch()
. To request a post-image, you setfullDocument
using the same method.Pre-images are written to the
config.system.preimages
collection.The
config.system.preimages
collection may become large. To limit the collection size, you can setexpireAfterSeconds
time for the pre-images as shown earlier.Pre-images are removed asynchronously by a background process.
Important
Backward-Incompatible Feature
Starting in MongoDB 6.0, if you are using document pre- and post-images
for change streams, you must disable
changeStreamPreAndPostImages for each collection using
the collMod
command before you can downgrade to an earlier
MongoDB version.
Tip
See also:
For change stream events and output, see Change Events.
To watch a collection for changes, see
db.collection.watch()
.For complete examples with the change stream output, see Change Streams with Document Pre- and Post-Images.
Example
The following example illustrates a delete
event:
{ "_id": { <Resume Token> }, "operationType": "delete", "clusterTime": <Timestamp>, "wallTime": <ISODate>, "ns": { "db": "engineering", "coll": "users" }, "documentKey": { "_id": ObjectId("599af247bb69cd89961c986d") } }
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.