$changeStream (aggregation)

Definition

$changeStream

Returns a Change Stream cursor on a collection, a database, or an entire cluster. Must be used as the first stage in an aggregation pipeline.

The $changeStream stage has the following syntax:

{
  $changeStream: {
    allChangesForCluster: <boolean>,
    fullDocument: <string>,
    resumeAfter: <int>
    startAfter: <document>
    startAtOperationTime: <timestamp>
  }
}

Parameter	Description
allChangesForCluster	Optional: Sets whether the change stream should include all changes in the cluster. May only be opened on the admin database.
fullDocument	Optional: Specifies whether change notifications include a copy of the full document when modified by update operations. default: Change notifications do not include the full document for update operations. updateLookup: Change notifications includes a copy of the document modified by the change. This document is the current majority-committed document or null if it no longer exists. In the case of partial updates, the change notification also provides a description of the change.
resumeAfter	Specifies a resume token as the logical starting point for the change stream. Cannot be used with startAfter or startAtOperationTime fields.
startAfter	Specifies a resume token as the logical starting point for the change stream. Cannot be used with resumeAfter or startAtOperationTime fields.
startAtOperationTime	Specifies a time as the logical starting point for the change stream. Cannot be used with resumeAfter or startAfter fields.

Examples

To create a change stream cursor using the aggregation stage, run the aggregate command.

var cur = db.names.aggregate( [
   { $changeStream: {} }
] )

To open the cursor, run cur.

When the change stream detects a change, the next() method returns a change event notification. For example, after running cur.next(), MongoDB returns a document similar to the following:

{
   "_id": {
      _data: "8262E2EE54000000022B022C0100296E5A100448E5E3DD01364019AE8FE8C6859527E046645F6964006462E2EE54C8756C0D5CF6F0720004"
   },
   "operationType": "insert",
   "clusterTime": Timestamp({ t: 1659039316, i: 2 }),
   "fullDocument": {
      "_id": ObjectId("62e2ee54c8756c0d5cf6f072"),
      "name": "Walker Percy"
   },
   "ns": {
      "db": "test",
      "coll": "names"
   },
   "documentKey": { _id: ObjectId("62e2ee54c8756c0d5cf6f072") }
}

For more information on change stream notifications, see Change Events.