How to get number of documents using Mongoose?

In Mongoose, the standard method for retrieving document counts is to use the Model.countDocuments() method. This approach is straightforward and allows you to count the number of documents in the database that meet specific criteria.

Here is an example demonstrating how to use countDocuments() on a model named User:

javascript
const mongoose = require('mongoose');

// First define the User model
const UserSchema = new mongoose.Schema({
  name: String,
  age: Number,
  // Other fields...
});
const User = mongoose.model('User', UserSchema);

// Connect to MongoDB
mongoose.connect('mongodb://localhost:27017/yourDatabase', {
  useNewUrlParser: true,
  useUnifiedTopology: true,
}).then(() => {
  console.log('Database connection successful');

  // Count all users
  User.countDocuments((err, count) => {
    if (err) {
      console.error('Error counting user count:', err);
    } else {
      console.log(`Total of ${count} users`);
    }
  });

  // Count users meeting specific conditions, such as those older than 20
  User.countDocuments({ age: { $gt: 20 } }, (err, count) => {
    if (err) {
      console.error('Error counting users older than 20:', err);
    } else {
      console.log(`Total of ${count} users older than 20`);
    }
  });

}).catch(err => {
  console.error('Database connection failed:', err);
});

In the above example, countDocuments() accepts two parameters. The first specifies the query condition (if omitted, it counts all documents in the collection), and the second is a callback function invoked upon completion. This callback receives two arguments: err and count. If successful, err is null and count holds the document count.

Note that for counting all documents without query conditions, you can pass the callback function as the first argument.

If you are using async/await, you can do the following:

javascript
async function countUsers() {
  try {
    const userCount = await User.countDocuments();
    console.log(`Total of ${userCount} users`);
  } catch (err) {
    console.error('Error counting user count:', err);
  }
}

countUsers();

In this example, countDocuments returns a Promise, enabling cleaner asynchronous handling with async/await.

To summarize, countDocuments() is the recommended method in Mongoose for obtaining document counts, allowing you to specify query conditions to count documents matching specific criteria.