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$changeStream

The `$changeStream` stage returns a change stream cursor that tracks changes to a collection. Change streams allow applications to access real-time data changes without the complexity and risk of tailing the oplog.

Syntax

{
  $changeStream: {
    fullDocument: <string>,
    fullDocumentBeforeChange: <string>,
    resumeAfter: <document>,
    startAfter: <document>,
    startAtOperationTime: <timestamp>
  }
}

Parameters

fullDocumentstring

Optional. Specifies whether to return the full document for update operations. Options: "updateLookup", "whenAvailable", "required".

fullDocumentBeforeChangestring

Optional. Specifies whether to return the full document as it was before the change. Options: "whenAvailable", "required", "off".

resumeAfterobject

Optional. A resume token to resume the change stream after a specific change event.

startAfterobject

Optional. A resume token to start the change stream after a specific event, even if the token is invalidated.

startAtOperationTimeobject

Optional. A timestamp to start the change stream from a specific point in time.

Examples

Sample Data

{
  "_id": "0fcc0bf0-ed18-4ab8-b558-9848e18058f4",
  "name": "First Up Consultants | Beverage Shop",
  "sales": { "totalSales": 75670 }
}

Watch for changes

Open a change stream to monitor all changes to the collection.

This query creates a change stream cursor for real-time updates.

Query:

db.stores.aggregate([
  { $changeStream: {} }
])

Output:

[
  {
    "_id": { "_data": "..." },
    "operationType": "insert",
    "fullDocument": {
      "_id": "new-store-id",
      "name": "New Store"
    }
  }
]

Watch with full document lookup

Monitor changes and return the full updated document.

This query includes the complete document after updates.

Query:

db.stores.aggregate([
  { $changeStream: { fullDocument: "updateLookup" } }
])

Output:

[
  {
    "_id": { "_data": "..." },
    "operationType": "update",
    "fullDocument": {
      "_id": "store-id",
      "name": "Updated Store Name",
      "sales": { "totalSales": 80000 }
    }
  }
]

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