$exists - Amazon DocumentDB
Example (MongoDB Shell)Code examples
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$exists

The $exists operator is used to check whether a field exists in a document or not. $exists particularly useful when working with sparse indexes in Amazon DocumentDB, where the indexed field may not be present in all documents.

To use a sparse index that you have created in a query, you must use the $exists clause on the fields that cover the index. If you omit $exists, Amazon DocumentDB will not use the sparse index for the query.

Parameters

  • field: The field name to check for existence.

  • value: A boolean value (true or false) that specifies whether the field should exist (true) or not exist (false) in the matching documents.

Example (MongoDB Shell)

The following example demonstrates the use of the $exists operator with a sparse index on the special_diets field in the food collection.

Create sample documents

db.food.insertMany([
  { _id: 1, name: "Apple", special_diets: ["vegetarian", "gluten-free"] },
  { _id: 2, name: "Broccoli" },
  { _id: 3, name: "Chicken", special_diets: ["dairy-free"] }
]);

Create a sparse index on the `special_diets` field

db.food.createIndex({ "special_diets": 1 }, { sparse: true, name: "special_diets_sparse_asc" });

Query example

db.food.find({ "special_diets": { $exists: true } });

Output

[
  { "_id" : 1, "name" : "Apple", "special_diets" : [ "vegetarian", "gluten-free" ] },
  { "_id" : 3, "name" : "Chicken", "special_diets" : [ "dairy-free" ] }
]

Code examples

To view a code example for using the $exists command, choose the tab for the language that you want to use:

Node.js
const { MongoClient } = require('mongodb');

async function main() {
  const client = await MongoClient.connect('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false');
  const db = client.db('test');
  const collection = db.collection('food');

  const result = await collection.find({ "special_diets": { $exists: true } }).toArray();
  console.log(result);

  await client.close();
}

main();
Python
import pymongo

client = pymongo.MongoClient('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false')
db = client['test']
collection = db['food']

result = list(collection.find({"special_diets": {"$exists": True}}))
print(result)

client.close()