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$elemMatch

The $elemMatch operator in Amazon DocumentDB is used to query an array field and return documents where at least one element in the array matches the specified criteria. This operator is particularly useful when you have complex data structures with nested arrays or embedded documents.

Planner version 2.0 added index support for $elemMatch.

Parameters

 

Using $elemMatch within an $all expression

See Using $elemMatch within an $all expression for limitations regarding the use of the $elemMatch operator within an $all expression.

Example (MongoDB Shell)

The following example demonstrates how to use the $elemMatch operator to find documents where the parts array has at least one element that matches the specified criteria.

Create sample documents

db.col.insertMany([
  { _id: 1, parts: [{ part: "xyz", qty: 10 }, { part: "abc", qty: 20 }] },
  { _id: 2, parts: [{ part: "xyz", qty: 5 }, { part: "abc", qty: 10 }] },
  { _id: 3, parts: [{ part: "xyz", qty: 15 }, { part: "abc", qty: 100 }] },
  { _id: 4, parts: [{ part: "abc", qty: 150 }] }
]);

Query example

db.col.find({
  parts: { "$elemMatch": { part: "xyz", qty: { $lt: 11 } } }
})

Output

{ "_id" : 1, "parts" : [ { "part" : "xyz", "qty" : 10 }, { "part" : "abc", "qty" : 20 } ] }
{ "_id" : 2, "parts" : [ { "part" : "xyz", "qty" : 5 }, { "part" : "abc", "qty" : 10 } ] }

Code examples

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

Node.js

const { MongoClient } = require('mongodb');

async function example() {
  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 col = db.collection('col');

  const result = await col.find({
    parts: { 
      "$elemMatch": { part: "xyz", qty: { $lt: 11 } } 
    }
  }).toArray();

  console.log(JSON.stringify(result, null, 2));
  await client.close();
}

example();

Python

from pymongo import MongoClient

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

    result = list(col.find({
      'parts': { 
        '$elemMatch': {'part': 'xyz', 'qty': {'$lt': 11}} 
      }
    }))

    print(result)
    client.close()

example()