Change Stream generated for UpdateOne Query On List Using Array Filters Is Not Consistent For Single and Multiple matches

Working with Data
, ,
1

Hi Team,

I am getting different formats of change streams for updateOne query on List element using Array filters for single and multiple matches.

  • When a single element is matched and modified, we get the expected difference in the form a dot separate paths along with the values before and after change.
  • When multiple elements are matched and modified, we get the entire list before and after the change.

Please find below example with the query and generated change stream:

Single Match:

db.getCollection("test").find({_id:1},{"list":1})[
  {
    _id: 1,
    list: [
      { key1: 'a', position: 1 },
      { key1: 'b', position: 2 }
    ]
  }
]

Query:

db.getCollection("test").updateMany(
{_id:1},
{"$set":{"list.$[element].position":3}},
{"arrayFilters":[{"element.key1":"a"}]})
{
  acknowledged: true,
  insertedId: null,
  matchedCount: 1,
  modifiedCount: 1,
  upsertedCount: 0
}

Updated Object:

db.getCollection("test").find({_id:1},{list:1})[
  {
    _id: 1,
    list: [
      { key1: 'a', position: 3 },
      { key1: 'b', position: 2 }
    ]
  }
]`

`

Change Stream generated:

[
  {
    operationType: 'update',
    clusterTime: Timestamp({ t: 1723030373, i: 20 }),
    wallTime: '2024-08-07T11:32:53.484Z',
    ns: { db: 'testDB', coll: 'test' },
    documentKey: { _id: '1' },
    updateDescription: {
      updatedFields: { 'list.2.position': 1 },
      removedFields: [],
      truncatedArrays: [],
      updatedFieldsBeforeChange: { 'list.2.position': 3 }
    }
  }
]

Multiple Match:

db.getCollection("test").find({_id:1},{"list":1})[
  {
    _id: 1,
    list: [
      { key1: 'a', position: 1 },
      { key1: 'b', position: 2 },
      { key1: 'a', position: 3 }
    ]
  }
]

Query:

db.getCollection("test").updateMany(
{_id:1},
{"$set":{"list.$[element].position":4}},
{"arrayFilters":[{"element.key1":"a"}]})
{
  acknowledged: true,
  insertedId: null,
  matchedCount: 1,
  modifiedCount: 1,
  upsertedCount: 0
}

Updated Object:

db.getCollection("test").find({_id:1},{list:1})[
  {
    _id: 1,
    list: [
      { key1: 'a', position: 4 },
      { key1: 'b', position: 2 },
      { key1: 'a', position: 4 }
    ]
  }
]

Change Stream generated:

[
  {
    _id: ObjectId("66b35945e6d6bb7b49b705f3"),
    operationType: 'update',
    clusterTime: Timestamp({ t: 1723029829, i: 8 }),
    wallTime: '2024-08-07T11:23:49.134Z',
    ns: { db: 'testDB', coll: 'test' },
    documentKey: { _id: 1 },
    updateDescription: {
      updatedFields: {
        list: [
          { key1: 'a', position: 1 },
          { key1: 'b', position: 2 },
          { key1: 'a', position: 3 }
        ]
      },
      removedFields: [],
      truncatedArrays: [],
      updatedFieldsBeforeChange: {
        list: [
          { key1: 'a', position: 4 },
          { key1: 'b', position: 2 },
          { key1: 'a', position: 4 }
        ]
      }
    }
  }
]