Document model mental model (JSON/BSON) in MongoDB - Mini Project: Build & Apply

Building a Simple MongoDB Document Model

📖 Scenario: You are creating a small database for a local bookstore. The store wants to keep track of books with details like title, author, and price.

🎯 Goal: Build a MongoDB document model using JSON/BSON format to represent books in the bookstore.

📋 What You'll Learn

Create a document representing a book with specific fields

Add a configuration field for currency

Use a query to find books cheaper than a certain price

Complete the document with an additional field for stock quantity

💡 Why This Matters

🌍 Real World

Document models like this are used in MongoDB to store and organize data for applications such as online stores, libraries, and inventory systems.

💼 Career

Understanding how to structure documents and write queries is essential for roles like database administrators, backend developers, and data engineers working with NoSQL databases.

1

Create the initial book document

Create a MongoDB document called book with these exact fields and values: title set to "The Great Gatsby", author set to "F. Scott Fitzgerald", and price set to 10.99.

MongoDB

# Create the book document with title, author, and price
# Your code here

Hint

Use curly braces to create a document and include the fields exactly as shown.

2

Add a currency field

Add a field called currency to the book document and set it to "USD".

MongoDB

book = {
  "title": "The Great Gatsby",
  "author": "F. Scott Fitzgerald",
  "price": 10.99
}
# Add the currency field below
# Your code here

Hint

Add the new field inside the existing document with a comma separating it from previous fields.

3

Query for books cheaper than a price

Write a MongoDB query called cheap_books_query that finds books with price less than 15.

MongoDB

book = {
  "title": "The Great Gatsby",
  "author": "F. Scott Fitzgerald",
  "price": 10.99,
  "currency": "USD"
}
# Create a query to find books with price less than 15
# Your code here

Hint

Use MongoDB's query operator $lt to find prices less than 15.

4

Add stock quantity to the book document

Add a field called stock to the book document and set it to 30.

MongoDB

book = {
  "title": "The Great Gatsby",
  "author": "F. Scott Fitzgerald",
  "price": 10.99,
  "currency": "USD"
}

cheap_books_query = { "price": { "$lt": 15 } }
# Add the stock field below
# Your code here

Hint

Add the stock field with a comma after the previous field inside the document.

Practice

1. Which of the following best describes a MongoDB document?

easy

A. A compiled program file

B. A table with rows and columns like in SQL

C. A set of key-value pairs similar to a JSON object

D. A flat file storing plain text data

Solution

1. Step 1: Understand MongoDB document structure

   MongoDB stores data as documents, which are collections of key-value pairs similar to JSON objects.

2. Step 2: Compare with other data formats

   Unlike tables or flat files, documents can store nested data and arrays, making them flexible and structured.

3. Final Answer:

   A set of key-value pairs similar to a JSON object -> Option C

4. Quick Check:

   Document = JSON-like key-value pairs [OK]

Hint: Think JSON object when you hear MongoDB document [OK]

Common Mistakes:

• Confusing documents with SQL tables
• Thinking documents are flat text files
• Assuming documents are executable files

2. Which of the following is the correct way to represent a nested document in MongoDB?

easy

A. { "name": "Alice", "address": { "city": "NY", "zip": 10001 } }

B. { "name": "Alice", "address": "city: NY, zip: 10001" }

C. { "name": "Alice", "address": ["city", "NY", "zip", 10001] }

D. { "name": "Alice", "address": ("city": "NY", "zip": 10001) }

Solution

1. Step 1: Identify correct JSON syntax for nested documents

   Nested documents are represented as objects inside another object using curly braces {} with key-value pairs.

2. Step 2: Check each option's syntax

   { "name": "Alice", "address": { "city": "NY", "zip": 10001 } } uses proper JSON syntax with nested braces. The other options use incorrect formats like strings, arrays, or parentheses.

3. Final Answer:

   { "name": "Alice", "address": { "city": "NY", "zip": 10001 } } -> Option A

4. Quick Check:

   Nested document = object inside object with braces [OK]

Hint: Nested documents use curly braces inside braces [OK]

Common Mistakes:

• Using strings instead of nested objects
• Using arrays for nested key-value pairs
• Using parentheses instead of braces

3. Given the document { "name": "Bob", "scores": [85, 90, 78] }, what is the value of the scores field?

medium

A. "85, 90, 78"

B. [85, 90, 78]

C. {85: true, 90: true, 78: true}

D. 85

Solution

1. Step 1: Identify the data type of the scores field

   The scores field contains square brackets [], which represent an array in JSON/BSON.

2. Step 2: Understand array representation

   The array holds the numbers 85, 90, and 78 as elements, so the value is the list [85, 90, 78].

3. Final Answer:

   [85, 90, 78] -> Option B

4. Quick Check:

   Square brackets = array = [85, 90, 78] [OK]

Hint: Square brackets mean array, not string or object [OK]

Common Mistakes:

• Confusing array with string
• Thinking array is a key-value object
• Selecting only one element instead of full array

4. Identify the error in this MongoDB document: { "title": "Book", "pages": "300", "author": { "name": "John", "age": 45 }

medium

A. Missing closing brace for the document

B. Pages field should be a number, not a string

C. Title field cannot be a string

D. Author name must be an array

Solution

1. Step 1: Check document syntax carefully

   The document starts with { but does not have a matching closing brace } at the end.

2. Step 2: Validate other fields

   While pages is a string, MongoDB allows strings for numbers; title as string is valid; author.name as string is valid.

3. Final Answer:

   Missing closing brace for the document -> Option A

4. Quick Check:

   Every { must have matching } [OK]

Hint: Count opening and closing braces carefully [OK]

Common Mistakes:

• Ignoring missing braces
• Thinking string numbers are invalid
• Assuming arrays are required for nested objects

5. You want to store a product with multiple colors and a supplier's contact info inside one MongoDB document. Which structure correctly models this?

hard

A. { "product": "Shirt", "colors": "red, blue", "supplier": "ABC Co, 123-456" }

B. { "product": "Shirt", "colors": ("red", "blue"), "supplier": { "name": "ABC Co", "phone": 123456 } }

C. { "product": "Shirt", "colors": { "red": true, "blue": true }, "supplier": ["ABC Co", "123-456"] }

D. { "product": "Shirt", "colors": ["red", "blue"], "supplier": { "name": "ABC Co", "phone": "123-456" } }

Solution

1. Step 1: Understand how to store multiple values and nested info

   Multiple colors should be stored as an array, and supplier info as a nested document with key-value pairs.

2. Step 2: Evaluate each option's structure

   { "product": "Shirt", "colors": ["red", "blue"], "supplier": { "name": "ABC Co", "phone": "123-456" } } correctly uses an array for colors and a nested document for supplier. { "product": "Shirt", "colors": "red, blue", "supplier": "ABC Co, 123-456" } uses strings instead of structured data. { "product": "Shirt", "colors": { "red": true, "blue": true }, "supplier": ["ABC Co", "123-456"] } uses an object for colors incorrectly and an array for supplier. { "product": "Shirt", "colors": ("red", "blue"), "supplier": { "name": "ABC Co", "phone": 123456 } } uses parentheses which are invalid in JSON.

3. Final Answer:

   { "product": "Shirt", "colors": ["red", "blue"], "supplier": { "name": "ABC Co", "phone": "123-456" } } -> Option D

4. Quick Check:

   Arrays for lists, objects for nested info [OK]

Hint: Use arrays for lists, objects for nested details [OK]

Common Mistakes:

• Using strings instead of arrays for multiple values
• Using invalid parentheses instead of braces
• Confusing arrays and objects for nested data