DOCSP-13958 add array trunc change stream field

Author: npentrel

source/reference/change-events.txt

@@ -1,4 +1,5 @@
 .. index:: changeStreams notification
+.. _change-events:
 
 =============
 Change Events
@@ -37,7 +38,11 @@ stream response document can have.
       "documentKey" : { "_id" : <value> },
       "updateDescription" : {
          "updatedFields" : { <document> },
-         "removedFields" : [ "<field>", ... ]
+         "removedFields" : [ "<field>", ... ],
+         "truncatedArrays" : [
+            { "field" : <field>, "newSize" : <integer> },
+            ...
+         ]
       }
       "clusterTime" : <Timestamp>,
       "txnNumber" : <NumberLong>,
@@ -170,6 +175,29 @@ following table describes each field in the change stream response document:
      - array
      - An array of fields that were removed by the update operation.
 
+   * - ``updateDescription.truncatedArrays``
+     - array
+     - An array of documents which record array truncations performed
+       with pipeline-based updates using one or more of the following
+       stages:
+
+       - :pipeline:`$addFields`
+       - :pipeline:`$set`
+       - :pipeline:`$replaceRoot`
+       - :pipeline:`$replaceWith`
+
+       .. note::
+
+          If the entire array is replaced, the truncations will be
+          reported under ``updateDescription.updatedFields``.
+
+   * - ``updateDescription.truncatedArrays.field``
+     - string
+     - The name of the truncated field.
+
+   * - ``updateDescription.truncatedArrays.newSize``
+     - integer
+     - The number of elements in the truncated array.
    * - ``clusterTime``
 
      - Timestamp
@@ -268,10 +296,14 @@ The following example illustrates an ``update`` event:
          updatedFields: {
             email: '[email protected]'
          },
-         removedFields: ['phoneNumber']
+         removedFields: ['phoneNumber'],
+         truncatedArrays: [ {
+            "field" : "vacation_time",
+            "newSize" : 36
+         } ]
       }
    }
-   
+
 The following example illustrates an ``update`` event for change streams
 opened with the ``fullDocument : updateLookup`` option:
 
@@ -292,7 +324,11 @@ opened with the ``fullDocument : updateLookup`` option:
          updatedFields: {
             email: '[email protected]'
          },
-         removedFields: ['phoneNumber']
+         removedFields: ['phoneNumber'],
+         truncatedArrays: [ {
+            "field" : "vacation_time",
+            "newSize" : 36
+         } ]
       },
       fullDocument: { 
          _id: ObjectId("58a4eb4a30c75625e00d2820"),

source/release-notes/5.0.txt

@@ -76,6 +76,15 @@ Projection
 Transactions
 ------------
 
+.. _5.0-rel-notes-change-streams:
+
+Change Streams
+--------------
+
+Starting in MongoDB 5.0, :ref:`change-events`
+contain the field ``updateDescription.truncatedArrays`` to record array
+truncations.
+
 .. _5.0-rel-notes-security:
 
 Security Improvements
@@ -153,7 +162,7 @@ Starting in MongoDB 5.0, the :dbcommand:`reIndex` command and the
 Schema Validation Failures Explained
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-MongoDB 5.0 adds detailed explanations when a document fails 
+MongoDB 5.0 adds detailed explanations when a document fails
 :ref:`schema validation <schema-validation-overview>`.
 
 Repair Option in ``validate`` Command