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mongodb / v3.6 / reference / reference-method-cursor.showRecordId.html

cursor.showRecordId()

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cursor. showRecordId ( )

Changed in version 3.2: This method replaces the previous cursor.showDiskLoc().

Modifies the output of a query by adding a field $recordId to matching documents. $recordId is the internal key which uniquely identifies a document in a collection. It has the form:

"$recordId": NumberLong(<int>)
Returns: A modified cursor object that contains documents with appended information describing the internal record key.

Example

The following operation appends the showRecordId() method to the db.collection.find() method in order to include storage engine record information in the matching documents:

db.collection.find( { a: 1 } ).showRecordId()

The operation returns the following documents, which include the $recordId field:

{
  "_id" : ObjectId("53908ccb18facd50a75bfbac"),
  "a" : 1,
  "b" : 1,
  "$recordId" : NumberLong(168112)
}
{
   "_id" : ObjectId("53908cd518facd50a75bfbad"),
   "a" : 1,
   "b" : 2,
   "$recordId" : NumberLong(168176)
}

You can project the added field $recordId, as in the following example:

db.collection.find( { a: 1 }, { $recordId: 1 } ).showRecordId()

This query returns only the _id field and the $recordId field in the matching documents:

{
  "_id" : ObjectId("53908ccb18facd50a75bfbac"),
  "$recordId" : NumberLong(168112)
}
{
   "_id" : ObjectId("53908cd518facd50a75bfbad"),
   "$recordId" : NumberLong(168176)
}