MongoDB with Deno - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to connect to MongoDB using Deno.

Deno

import { MongoClient } from "https://deno.land/x/mongo@v0.31.1/mod.ts";

const client = new MongoClient();
await client.[1]("mongodb://localhost:27017");

Drag options to blanks, or click blank then click option'

Aopen

Bconnect

Cstart

DconnectTo

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method that does not exist like 'open' or 'start'.

The connect method is used to establish a connection to the MongoDB server.

2fill in blank

medium

Complete the code to select the database named 'testdb'.

Deno

const db = client.[1]("testdb");

Drag options to blanks, or click blank then click option'

AgetDatabase

Bdb

Cdatabase

DselectDb

Attempts:

3 left

💡 Hint

Common Mistakes

Using methods that do not exist or are not part of the API.

The database method is used to select a database by name in Deno MongoDB client.

3fill in blank

hard

Fix the error in the code to get a collection named 'users'.

Deno

const users = db.[1]("users");

Drag options to blanks, or click blank then click option'

AgetCollections

Bcollections

CgetCollection

Dcollection

Attempts:

3 left

💡 Hint

Common Mistakes

Using plural or incorrect method names like 'collections' or 'getCollection'.

The correct method to get a collection is collection. Other options are incorrect or do not exist.

4fill in blank

hard

Fill both blanks to insert a document with name 'Alice' and age 30 into the 'users' collection.

Deno

await users.[1]({ name: "Alice", age: [2] });

Drag options to blanks, or click blank then click option'

AinsertOne

BinsertMany

C30

D25

Attempts:

3 left

💡 Hint

Common Mistakes

Using insertMany for a single document or wrong age value.

Use insertOne to insert a single document. The age value should be 30 as given.

5fill in blank

hard

Fill all three blanks to find all users older than 25 and print their names.

Deno

const cursor = users.[1]({ age: { [2]: [3] } });
for await (const user of cursor) {
  console.log(user.name);
}

Drag options to blanks, or click blank then click option'

Afind

B$gt

C25

D$lt

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong operators like $lt or wrong method names.

The find method queries documents. The operator $gt means 'greater than'. We want age greater than 25.

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