> For the complete MongoDB documentation index, see www.mongodb.com/docs/llms.txt

# cursor.returnKey() (mongosh method)

## Definition

**Important: mongosh Method**

This page documents a [`mongosh`](https://www.mongodb.com/docs/mongodb-shell.md#mongodb-binary-bin.mongosh) method. This is *not* the documentation for a language-specific driver, such as Node.js.

For MongoDB API drivers, refer to the language-specific [MongoDB driver documentation.](https://www.mongodb.com/docs/drivers/)

**Tip:**

[`$meta`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/meta.md#mongodb-expression-exp.-meta) supports the keyword `"indexKey"` to return index key metadata if an index is used. The use of [`{ $meta: "indexKey" }`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/meta.md#mongodb-expression-exp.-meta) is preferred over [`cursor.returnKey()`.](https://www.mongodb.com/docs/manual/reference/method/cursor.returnkey.md#mongodb-method-cursor.returnKey)

Modifies the cursor to return index keys rather than the documents.

The [`cursor.returnKey()`](https://www.mongodb.com/docs/manual/reference/method/cursor.returnkey.md#mongodb-method-cursor.returnKey) has the following form:

```javascript
cursor.returnKey()
```

The [cursor](https://www.mongodb.com/docs/manual/core/cursors.md#std-label-cursors) that [`returnKey()`](https://www.mongodb.com/docs/manual/reference/method/cursor.returnkey.md#mongodb-method-cursor.returnKey) is attached to with a modified result set. This allows for additional cursor modifiers to be chained.

## Compatibility

This method is available in deployments hosted in the following environments:

- [MongoDB Atlas](https://www.mongodb.com/docs/atlas): The fully managed service for MongoDB deployments in the cloud

**Note:**

This command is supported in all MongoDB Atlas clusters. For information on Atlas support for all commands, see [Unsupported Commands.](https://www.mongodb.com/docs/atlas/unsupported-commands/)

- [MongoDB Enterprise](https://www.mongodb.com/docs/manual/administration/install-enterprise.md#std-label-install-mdb-enterprise): The subscription-based, self-managed version of MongoDB

- [MongoDB Community](https://www.mongodb.com/docs/manual/administration/install-community.md#std-label-install-mdb-community-edition): The source-available, free-to-use, and self-managed version of MongoDB

## Behavior

If the query does not use an index to perform the read operation, the cursor returns empty documents.

## Example

The `restaurants` collection contains documents with the following schema:

```javascript
db.restaurants.insertOne(
   {
      _id: ObjectId("564f3a35b385149fc7e3fab9"),
      address: {
         building: "2780",
         coord: [
            -73.98241999999999,
            40.579505
         ],
         street: "Stillwell Avenue",
         zipcode: "11224"
      },
      borough: "Brooklyn",
      cuisine: "American ",
      grades: [
         {
            date: ISODate("2014-06-10T00:00:00Z"),
            grade: "A",
            score: 5
         },
         {
            date: ISODate("2013-06-05T00:00:00Z"),
            grade: "A",
            score: 7
         }
      ],
      name: "Riviera Caterer",
      restaurant_id: "40356018"
   }
)
```

The collection has two indexes in addition to the default `_id` index:

```javascript
{
   "v" : 1,
   "key" : {
      "_id" : 1
   },
   "name" : "_id_",
   "ns" : "guidebook.restaurant"
},
{
   "v" : 1,
   "key" : {
      "cuisine" : 1
   },
   "name" : "cuisine_1",
   "ns" : "guidebook.restaurant"
},
{
   "v" : 1,
   "key" : {
      "_fts" : "text",
      "_ftsx" : 1
   },
   "name" : "name_text",
   "ns" : "guidebook.restaurant",
   "weights" : {
      "name" : 1
   },
   "default_language" : "english",
   "language_override" : "language",
   "textIndexVersion" : 3
}
```

The following code uses the [`cursor.returnKey()`](https://www.mongodb.com/docs/manual/reference/method/cursor.returnkey.md#mongodb-method-cursor.returnKey) method to return only the indexed fields used for executing the query:

```javascript
var csr = db.restaurant.find( { "cuisine" : "Japanese" } )
csr.returnKey()
```

This returns the following:

```javascript
{ "cuisine" : "Japanese" }
{ "cuisine" : "Japanese" }
{ "cuisine" : "Japanese" }
{ "cuisine" : "Japanese" }
...
```