Dot notation for embedded documents in MongoDB - Mini Project: Build & Apply

Dot notation for embedded documents

📖 Scenario: You are managing a small library database. Each book has a title and an embedded document for the author details, including the author's name and birth year.

🎯 Goal: You will create a collection of books with embedded author documents. Then, you will write queries using dot notation to access the author's name and birth year.

📋 What You'll Learn

Create a collection called books with three documents.

Each document must have a title field and an embedded author document with name and birthYear fields.

Create a variable called authorNameField that stores the string for accessing the author's name using dot notation.

Write a query that finds all books and projects only the title and the author's name using the authorNameField variable.

Write a query that finds all books and projects only the title and the author's birth year using dot notation directly.

💡 Why This Matters

🌍 Real World

Embedded documents are common in MongoDB to store related data together, like author details inside a book document.

💼 Career

Understanding dot notation helps you query and manipulate nested data efficiently in NoSQL databases like MongoDB, a valuable skill for backend and database developers.

1

Create the books collection with embedded author documents

Create a variable called books and assign it an array of three documents. Each document should have a title string and an author embedded document with name and birthYear fields exactly as follows: { title: "Book One", author: { name: "Alice", birthYear: 1970 } }, { title: "Book Two", author: { name: "Bob", birthYear: 1980 } }, and { title: "Book Three", author: { name: "Charlie", birthYear: 1990 } }.

MongoDB

# Create the books array with embedded author documents
# Your code here

Hint

Use an array of objects. Each object has a title and an author object with name and birthYear.

2

Create a variable for the author's name field using dot notation

Create a variable called authorNameField and assign it the string "author.name" to represent the dot notation path to the author's name.

MongoDB

books = [
    { title: "Book One", author: { name: "Alice", birthYear: 1970 } },
    { title: "Book Two", author: { name: "Bob", birthYear: 1980 } },
    { title: "Book Three", author: { name: "Charlie", birthYear: 1990 } }
]
# Create authorNameField variable with string "author.name"
# Your code here

Hint

Assign the string "author.name" to the variable authorNameField.

3

Write a query to find all books projecting title and author's name using the variable

Write a query called queryAuthorNames that uses books.find() with an empty filter {} and a projection object that includes title: 1 and uses the authorNameField variable as a key with value 1 to project the author's name.

MongoDB

books = [
    { title: "Book One", author: { name: "Alice", birthYear: 1970 } },
    { title: "Book Two", author: { name: "Bob", birthYear: 1980 } },
    { title: "Book Three", author: { name: "Charlie", birthYear: 1990 } }
]
authorNameField = "author.name"
# Write queryAuthorNames using books.find with projection of title and authorNameField
# Your code here

Hint

Use bracket notation [authorNameField] to use the variable as a key in the projection object.

4

Write a query to find all books projecting title and author's birth year using dot notation

Write a query called queryAuthorBirthYears that uses books.find() with an empty filter {} and a projection object that includes title: 1 and "author.birthYear": 1 to project the author's birth year using dot notation directly.

MongoDB

books = [
    { title: "Book One", author: { name: "Alice", birthYear: 1970 } },
    { title: "Book Two", author: { name: "Bob", birthYear: 1980 } },
    { title: "Book Three", author: { name: "Charlie", birthYear: 1990 } }
]
authorNameField = "author.name"
queryAuthorNames = books.find({}, { title: 1, [authorNameField]: 1 })
# Write queryAuthorBirthYears using books.find with projection of title and "author.birthYear"
# Your code here

Hint

Use the string "author.birthYear" directly as a key in the projection object.

Practice

1. What does dot notation in MongoDB allow you to do with embedded documents?

easy

A. Access nested fields inside embedded documents

B. Create new collections automatically

C. Encrypt data within documents

D. Delete entire databases

Solution

1. Step 1: Understand dot notation purpose

   Dot notation is used to reach inside nested or embedded documents to access specific fields.

2. Step 2: Compare with other options

   Creating collections, encrypting data, or deleting databases are unrelated to dot notation.

3. Final Answer:

   Access nested fields inside embedded documents -> Option A

4. Quick Check:

   Dot notation = Access nested fields [OK]

Hint: Dot notation accesses nested fields using dots [OK]

Common Mistakes:

• Thinking dot notation creates collections
• Confusing dot notation with encryption
• Assuming dot notation deletes data

2. Which of the following is the correct syntax to query the field address.city in MongoDB?

easy

A. { address.city: 'New York' }

B. { address->city: 'New York' }

C. { 'address.city': 'New York' }

D. { address[city]: 'New York' }

Solution

1. Step 1: Understand dot notation syntax in queries

   Field names with dots must be quoted as a single string in MongoDB queries.

2. Step 2: Evaluate each option

   { 'address.city': 'New York' } uses quotes correctly around 'address.city'. Options A, C, and D use invalid syntax.

3. Final Answer:

   { 'address.city': 'New York' } -> Option C

4. Quick Check:

   Quotes needed for dot field names = { 'address.city': 'New York' } [OK]

Hint: Quote dot notation keys in queries [OK]

Common Mistakes:

• Not quoting dot notation keys
• Using arrows or brackets instead of dots
• Using unquoted keys with dots

3. Given the collection documents:

{ name: 'Alice', contact: { phone: '1234', email: '[e-mail]' } }

What will the query db.collection.find({ 'contact.phone': '1234' }) return?

medium

A. Documents where contact.phone equals '1234'

B. Documents where contact.email equals '1234'

C. Documents where name equals '1234'

D. No documents, syntax error

Solution

1. Step 1: Understand the query filter

   The query filters documents where the embedded field contact.phone equals '1234'.

2. Step 2: Match with document data

   The example document has contact.phone as '1234', so it matches and will be returned.

3. Final Answer:

   Documents where contact.phone equals '1234' -> Option A

4. Quick Check:

   Dot notation filters embedded fields = Documents where contact.phone equals '1234' [OK]

Hint: Dot notation filters nested fields directly [OK]

Common Mistakes:

• Confusing phone with email field
• Thinking dot notation causes syntax error
• Assuming it filters top-level fields only

4. What is wrong with this MongoDB query to update the city in an embedded address document?

db.users.updateOne({ name: 'Bob' }, { $set: { address.city: 'Boston' } })

medium

A. Update operator $set is incorrect

B. Field name with dot must be quoted as a string

C. Collection name should be 'user' not 'users'

D. Query filter is missing

Solution

1. Step 1: Check update syntax for embedded fields

   When using dot notation in update keys, the field name must be quoted as a string.

2. Step 2: Analyze the given query

   The query uses address.city without quotes, which causes a syntax error.

3. Final Answer:

   Field name with dot must be quoted as a string -> Option B

4. Quick Check:

   Quote dot notation keys in updates = Field name with dot must be quoted as a string [OK]

Hint: Quote dot notation keys in update documents [OK]

Common Mistakes:

• Not quoting dot notation keys in $set
• Misusing update operators
• Assuming collection name is wrong

5. You have documents with nested structure:

{ _id: 1, profile: { name: 'Eve', contacts: { email: '[e-mail]', phone: '555' } } }

How do you write a query to find documents where the phone number is '555' using dot notation?

hard

A. { 'profile.contacts': { phone: '555' } }

B. { profile.contacts.phone: '555' }

C. { profile.contacts['phone']: '555' }

D. { 'profile.contacts.phone': '555' }

Solution

1. Step 1: Identify the full path to the nested field

   The phone field is inside contacts, which is inside profile, so the path is profile.contacts.phone.

2. Step 2: Use dot notation with quotes in query

   To query nested fields, use quotes around the full dot notation key: 'profile.contacts.phone'.

3. Final Answer:

   { 'profile.contacts.phone': '555' } -> Option D

4. Quick Check:

   Quote full dot notation path in query = { 'profile.contacts.phone': '555' } [OK]

Hint: Quote full dot notation path in queries [OK]

Common Mistakes:

• Not quoting dot notation keys
• Using object instead of dot notation in query
• Using brackets inside dot notation keys