MongoDB with Deno - Mini Project: Build & Apply

MongoDB with Deno: Simple User Data Storage

📖 Scenario: You are building a simple user management system using Deno and MongoDB. You want to store user information such as name and email in a MongoDB collection.

🎯 Goal: Build a Deno script that connects to MongoDB, creates a users collection, inserts user data, and queries the collection.

📋 What You'll Learn

Create a MongoDB client connection using Deno.

Define a database and a collection named users.

Insert multiple user documents with name and email fields.

Query the users collection to find users with a specific email domain.

💡 Why This Matters

🌍 Real World

Storing and querying user data is common in web applications, such as user profiles or contact lists.

💼 Career

Understanding how to connect Deno with MongoDB and perform basic CRUD operations is valuable for backend development roles.

1

Setup MongoDB Client Connection

Import MongoClient from "https://deno.land/x/mongo@0.31.1/mod.ts" and create a new MongoClient instance called client. Connect client to MongoDB at "mongodb://127.0.0.1:27017".

Deno

import { MongoClient } from "https://deno.land/x/mongo@0.31.1/mod.ts"

// Your code here

Hint

Use new MongoClient() to create the client and await client.connect() to connect.

2

Define Database and Collection

Create a variable called db that selects the database named "userdb" from client. Then create a variable called users that selects the collection named "users" from db.

Deno

import { MongoClient } from "https://deno.land/x/mongo@0.31.1/mod.ts"

const client = new MongoClient()
await client.connect("mongodb://127.0.0.1:27017")

// Your code here

Hint

Use client.database("userdb") and then db.collection("users").

3

Insert Multiple User Documents

Insert these three user documents into the users collection using insertMany: { name: "Alice", email: "[e-mail]" }, { name: "Bob", email: "[e-mail]" }, and { name: "Carol", email: "[e-mail]" }.

Deno

import { MongoClient } from "https://deno.land/x/mongo@0.31.1/mod.ts"

const client = new MongoClient()
await client.connect("mongodb://127.0.0.1:27017")

const db = client.database("userdb")
const users = db.collection("users")

// Your code here

Hint

Use await users.insertMany([...]) with the exact user objects.

4

Query Users by Email Domain

Create a variable called exampleUsers that finds all users in users collection whose email ends with "@example.com" using find with a regular expression filter.

Deno

import { MongoClient } from "https://deno.land/x/mongo@0.31.1/mod.ts"

const client = new MongoClient()
await client.connect("mongodb://127.0.0.1:27017")

const db = client.database("userdb")
const users = db.collection("users")

await users.insertMany([
  { name: "Alice", email: "[e-mail]" },
  { name: "Bob", email: "[e-mail]" },
  { name: "Carol", email: "[e-mail]" }
])

// Your code here

Hint

Use users.find({ email: { $regex: /@example\.com$/ } }) and convert to array with toArray().

Practice

1. What is the primary way MongoDB stores data when used with Deno?

easy

A. In collections of documents

B. In tables with rows and columns

C. As key-value pairs in a flat file

D. In XML files

Solution

1. Step 1: Understand MongoDB data structure

   MongoDB stores data in collections, which are groups of documents.

2. Step 2: Compare with other storage types

   Unlike SQL databases, MongoDB does not use tables but uses collections of JSON-like documents.

3. Final Answer:

   In collections of documents -> Option A

4. Quick Check:

   MongoDB = collections of documents [OK]

Hint: Remember MongoDB uses collections, not tables [OK]

Common Mistakes:

• Confusing MongoDB with SQL tables
• Thinking MongoDB stores data in flat files
• Assuming XML storage

2. Which of the following is the correct way to create a MongoClient instance in Deno?

easy

A. const client = new mongo.Client();

B. const client = MongoClient();

C. const client = mongoClient();

D. const client = new MongoClient();

Solution

1. Step 1: Check MongoClient instantiation syntax

   In Deno, you create a new MongoClient instance using the 'new' keyword and the exact class name 'MongoClient'.

2. Step 2: Validate option correctness

   const client = new MongoClient(); uses 'new MongoClient()', which is correct. Other options have incorrect casing or missing 'new'.

3. Final Answer:

   const client = new MongoClient(); -> Option D

4. Quick Check:

   Use 'new MongoClient()' to create client [OK]

Hint: Use 'new' keyword with exact class name MongoClient [OK]

Common Mistakes:

• Omitting 'new' keyword
• Wrong casing in 'MongoClient'
• Using incorrect module or variable names

3. Given the following Deno MongoDB code snippet, what will be the output?

const client = new MongoClient();
await client.connect("mongodb://localhost:27017");
const db = client.database("testdb");
const users = db.collection("users");

await users.insertOne({ name: "Alice", age: 30 });
const user = await users.findOne({ name: "Alice" });
console.log(user?.age);

medium

A. undefined

B. null

C. 30

D. Error: user not found

Solution

1. Step 1: Insert a document and then find it

   The code inserts a user document with name 'Alice' and age 30, then queries for that user.

2. Step 2: Access the age field from the found document

   The findOne call returns the document, so user?.age is 30, which is logged.

3. Final Answer:

   30 -> Option C

4. Quick Check:

   Inserted age 30, found age 30 [OK]

Hint: Inserted document fields appear in findOne result [OK]

Common Mistakes:

• Assuming findOne returns undefined if document exists
• Confusing null and undefined
• Forgetting to await async calls

4. Identify the error in this Deno MongoDB code snippet:

const client = new MongoClient();
client.connect("mongodb://localhost:27017");
const db = client.database("testdb");
const users = db.collection("users");
await users.insertOne({ name: "Bob" });

medium

A. Missing await before client.connect

B. Wrong method name 'database' instead of 'db'

C. insertOne should not be awaited

D. MongoClient cannot connect to localhost

Solution

1. Step 1: Check async connection call

   The connect method returns a promise and must be awaited to ensure connection before proceeding.

2. Step 2: Validate other code parts

   Method 'database' is correct, insertOne is async and should be awaited, and MongoClient can connect to localhost.

3. Final Answer:

   Missing await before client.connect -> Option A

4. Quick Check:

   Always await async connect calls [OK]

Hint: Always await async connect calls [OK]

Common Mistakes:

• Forgetting await on async connect
• Confusing method names
• Not awaiting insertOne

5. You want to insert multiple user documents in a MongoDB collection using Deno. Which approach correctly inserts multiple documents efficiently?

hard

A. Use insertOne in a loop for each document

B. Use insertMany with an array of documents

C. Call insertOne once with an array of documents

D. Use findOne to insert documents

Solution

1. Step 1: Understand bulk insert methods

   insertMany is designed to insert multiple documents at once efficiently.

2. Step 2: Compare options

   insertOne inserts a single document; calling it in a loop is inefficient. insertOne cannot take an array. findOne is for querying, not inserting.

3. Final Answer:

   Use insertMany with an array of documents -> Option B

4. Quick Check:

   Bulk insert = insertMany [OK]

Hint: Use insertMany for multiple documents at once [OK]

Common Mistakes:

• Using insertOne repeatedly instead of insertMany
• Passing array to insertOne
• Confusing findOne with insert methods