MongoDB Mongoose Match By Ids

Mongoose is a popular Object Document Mapping (ODM) library for MongoDB in Node.js. It provides a simple and elegant way to define schemas, models, and relationships between different collections in the database. One of the common use cases in working with MongoDB is to retrieve documents by their ids.

In this tutorial, we will explore how to query documents by their ids using Mongoose in Node.js.

Prerequisites

Before we get started, make sure that you have the following software installed on your system:

• Node.js and NPM
• MongoDB

If you have not installed MongoDB, please visit https://www.mongodb.com/ to download and install the latest version.

Next, create a new Node.js project with the following command:

mkdir mongoose-match-by-ids
cd mongoose-match-by-ids
npm init -y

Install the required dependencies:

npm install mongoose

Setting up the Database Connection

To connect to MongoDB, we need to create a new Mongoose instance and configure it for our database:

const mongoose = require('mongoose');

const dbURI = 'mongodb://localhost/mongoose-match-by-ids';

mongoose.connect(dbURI, {
  useNewUrlParser: true,
  useUnifiedTopology: true,
});

mongoose.connection.on('connected', () => {
  console.log(`Connected to MongoDB at ${dbURI}`);
});

mongoose.connection.on('error', (err) => {
  console.error(`Failed to connect to MongoDB: ${err}`);
});

Here, we create a new Mongoose instance and call the connect method to connect to the mongoose-match-by-ids database. We also specify options to use the new URL parser and the new server discovery and monitoring engine introduced in Mongoose 5.

Defining the Schema and Model

Now, let's define a simple schema for a user document that has name and email fields:

const userSchema = new mongoose.Schema({
  name: String,
  email: String,
});

const User = mongoose.model('User', userSchema);

Here, we create a new mongoose.Schema instance and define the fields for the user document. We then create a new mongoose.model instance for the User collection with the schema we just defined.

Creating and Retrieving Documents

Before we can query documents, let's create some sample documents in the User collection:

const users = await User.create([
  { name: 'John Doe', email: 'john.doe@example.com' },
  { name: 'Jane Doe', email: 'jane.doe@example.com' },
]);

Here, we use the User.create method to create two new documents in the User collection.

Next, let's retrieve a single document by its id:

const userId = users[0]._id;

const user = await User.findById(userId);

console.log(user); // { _id: ..., name: 'John Doe', email: 'john.doe@example.com' }

Here, we retrieve the first document in the users array and use its _id field to query the User collection. We use the User.findById method to retrieve the document by its id.

Retrieving Multiple Documents by Ids

To retrieve multiple documents by their ids, we can use the User.find method with a query object that specifies the ids we want to retrieve:

const userIds = users.map((user) => user._id);

const users = await User.find({ _id: { $in: userIds } });

console.log(users); // [{ _id: ..., name: 'John Doe', email: 'john.doe@example.com' }, { ... }]

Here, we create an array of user ids by mapping the _id field of each user document in the users array. We then use the $in operator in the query object to retrieve all documents that have an _id field that matches any of the ids in the userIds array.

Conclusion

In this tutorial, we explored how to query documents by their ids using Mongoose in Node.js. We learned how to connect to MongoDB, define a schema and model, create and retrieve documents, and retrieve multiple documents by their ids.

Code snippets are formatted as follows:

// this is a code snippet
const foo = 'bar';