MongoDB with Deno - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is MongoDB?

MongoDB is a database that stores data in flexible, JSON-like documents instead of tables. It is easy to use and good for storing data that changes often.

beginner

How do you connect to MongoDB in Deno?

You use a MongoDB client library for Deno, like 'deno_mongo'. You create a client with the database URL, then connect to the database to start working with data.

beginner

What is a collection in MongoDB?

A collection is like a folder that holds many documents (records). It is similar to a table in other databases but more flexible.

beginner

How do you insert a document into a MongoDB collection using Deno?

You call the 'insertOne' method on the collection object and pass the document (data) you want to add. This saves the document in the collection.

beginner

Why is MongoDB good for beginners learning databases with Deno?

Because MongoDB uses JSON-like documents, it feels like working with regular JavaScript objects. This makes it easy to understand and use with Deno, which also uses JavaScript/TypeScript.

Which command connects Deno to a MongoDB database?

A openMongo()

B connectToDatabase()

C new MongoClient()

D createConnection()

In Deno, you create a new MongoClient instance to connect to MongoDB.

In MongoDB, what is a 'collection'?

A A single data record

B A group of documents

C A database user

D A query command

A collection is a group of documents, similar to a table in other databases.

Which method adds a new document to a MongoDB collection in Deno?

A push()

B addDocument()

C save()

D insertOne()

The 'insertOne()' method inserts a single document into a collection.

What format does MongoDB use to store data?

A JSON-like documents

B XML files

C Tables with rows and columns

D Plain text files

MongoDB stores data as JSON-like documents, which are flexible and easy to use.

Why is MongoDB a good choice for Deno beginners?

A It stores data like JavaScript objects

B It uses SQL queries

C It requires no connection

D It only works with Deno

MongoDB stores data in a way similar to JavaScript objects, making it easy for Deno users to work with.

Explain how to connect to a MongoDB database using Deno and insert a simple document.

Think about the steps from creating a client to saving data.

Describe what a MongoDB collection is and how it compares to tables in other databases.

Focus on the structure and flexibility differences.

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