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Count Documents

Note

If you specify a callback method, countDocuments() and estimatedDocumentCount() return nothing. If you do not specify one, this method returns a Promise that resolves to the result object when it completes. See our guide on Promises and Callbacks for more information. See the countCallback() API documentation for information on how to use the result object.

The Node.js driver provides two methods for counting documents in a collection:

  • collection.countDocuments() returns the number of documents in the collection that match the specified query. If you specify an empty query document, countDocuments() returns the total number of documents in the collection.

  • collection.estimatedDocumentCount() returns an estimation of the number of documents in the collection based on collection metadata.

estimatedDocumentCount() is faster than countDocuments() because the estimation uses the collection's metadata rather than scanning the collection. In contrast, countDocuments() takes longer to return, but provides an accurate count of the number of documents and supports specifying a filter. Choose the appropriate method for your workload.

To specify which documents you wish to count, countDocuments() accepts a query parameter. countDocuments() counts the documents that match the specified query.

countDocuments() and estimatedDocumentCount() support optional settings that affect the method's execution. Refer to the reference documentation for each method for more information.

Tip

You can improve performance when using countDocuments() to return the total number of documents in a collection by avoiding a collection scan. To do this, use a hint to take advantage of the built-in index on the _id field. Use this technique only when calling countDocuments() with an empty query parameter.

collection.countDocuments({}, { hint: "_id_" });

Example

The following example estimates the number of documents in the movies collection in the sample_mflix database, and then returns an accurate count of the number of documents in the movies collection with Canada in the countries field.

Note

This example connects to an instance of MongoDB and uses a sample data database. To learn more about connecting to your MongoDB instance and loading this database, see the Usage Examples guide.

const { MongoClient } = require("mongodb");
// Replace the uri string with your MongoDB deployment's connection string.
const uri =
  "mongodb+srv://<user>:<password>@<cluster-url>?writeConcern=majority";
const client = new MongoClient(uri, {
  useNewUrlParser: true,
  useUnifiedTopology: true,
});
async function run() {
  try {
    await client.connect();
    const database = client.db("sample_mflix");
    const movies = database.collection("movies");
    // Estimate the total number of documents in the collection
    // and print out the count.
    const estimate = await movies.estimatedDocumentCount();
    console.log(`Estimated number of documents in the movies collection: ${estimate}`);
    // Query for movies from Canada.
    const query = { countries: "Canada" };
    // Find the number of documents that match the specified
    // query, (i.e. with "Canada" as a value in the "countries" field)
    // and print out the count.
    const countCanada = await movies.countDocuments(query);
    console.log(`Number of movies from Canada: ${countCanada}`);
  } finally {
    await client.close();
  }
}
run().catch(console.dir);

If you run the sample code above, you should see output that resembles the following:

Estimated number of documents in the movies collection: 23541
Number of movies from Canada: 1349
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