Querying nested fields at any depth in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find documents where the nested field 'address.city' equals 'Paris'.

MongoDB

db.users.find({"address[1]city": "Paris"})

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

A.

B$

C#

D_

Attempts:

3 left

💡 Hint

Common Mistakes

Using '$' instead of '.' to access nested fields.

Trying to access nested fields without quotes.

Using underscore '_' instead of dot '.' in field names.

In MongoDB, nested fields are accessed using dot notation. So to query the city inside address, use 'address.city'.

2fill in blank

medium

Complete the code to find documents where the nested field 'profile.details.age' is greater than 30.

MongoDB

db.users.find({"profile.details.age": { [1]: 30 }})

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

A$ne

B$lt

C$eq

D$gt

Attempts:

3 left

💡 Hint

Common Mistakes

Using '$lt' which means 'less than' instead of 'greater than'.

Using '$eq' which means 'equals' instead of a comparison operator.

Forgetting the dollar sign in the operator.

The operator '$gt' means 'greater than' in MongoDB queries. It filters documents where the field value is greater than the specified number.

3fill in blank

hard

Fix the error in the query to find documents where 'settings.notifications.email' is true.

MongoDB

db.users.find({"settings[1]notifications[1]email": true})

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

A.

B,

C:

D$

Attempts:

3 left

💡 Hint

Common Mistakes

Using commas or colons instead of dots.

Using dollar signs incorrectly in field names.

Not quoting the full nested field path.

To access nested fields at any depth, MongoDB requires dot notation between each level. So use '.' between 'settings', 'notifications', and 'email'.

4fill in blank

hard

Fill both blanks to query documents where 'profile.contacts.phone.mobile' exists and is not null.

MongoDB

db.users.find({"profile[1]contacts[2]phone.mobile": { $exists: true, $ne: null } })

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

A.

B$

C_

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing different separators between nested fields.

Using underscores or dashes instead of dots.

Leaving out separators between nested fields.

Use dot notation '.' between each nested field to correctly access 'profile.contacts.phone.mobile'.

5fill in blank

hard

Fill all three blanks to query documents where 'settings.preferences.theme.color' equals 'dark'.

MongoDB

db.users.find({"settings[1]preferences[2]theme[3]color": "dark"})

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

A.

B$

C_

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using different separators like '$' or '_' instead of '.'

Mixing separators inconsistently.

Not using any separator between nested fields.

Dot notation '.' is used to access nested fields at any depth in MongoDB queries.

Practice

1. Which MongoDB query syntax correctly accesses a nested field named address.city inside a document?

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 for nested fields

   MongoDB uses dot notation like "address.city" to access nested fields inside documents.

2. Step 2: Identify correct query syntax

   The correct query uses a string key with dot notation: { "address.city": "New York" }.

3. Final Answer:

   { "address.city": "New York" } -> Option D

4. Quick Check:

   Dot notation = { "address.city": value } [OK]

Hint: Use quotes and dot notation to access nested fields [OK]

Common Mistakes:

• Using nested objects instead of dot notation in query
• Using arrow or parentheses instead of dot notation
• Not quoting the nested field path

2. Which of the following is the correct MongoDB query to find documents where the nested field profile.details.age equals 30?

easy

A. { profile.details.age = 30 }

B. { "profile.details.age": 30 }

C. { profile.details.age: 30 }

D. { 'profile.details.age' == 30 }

Solution

1. Step 1: Use string keys with dot notation in MongoDB queries

   MongoDB requires the nested field path as a string key with dots, like "profile.details.age".

2. Step 2: Use colon for key-value pairs in query objects

   The correct syntax uses colon (:), not equals (=) or double equals (==), so { "profile.details.age": 30 } is correct.

3. Final Answer:

   { "profile.details.age": 30 } -> Option B

4. Quick Check:

   Dot notation with colon = correct query [OK]

Hint: Use colon and quotes for nested keys in queries [OK]

Common Mistakes:

• Using = or == instead of colon in query
• Not quoting the nested field path
• Using object notation instead of dot notation

3. Given the collection documents:

{ "user": { "contact": { "email": "[e-mail]" } } }, { "user": { "contact": { "email": "[e-mail]" } } }, { "user": { "contact": { "phone": "12345" } } }

What will the query db.collection.find({ "user.contact.email": { $exists: true } }) return?

medium

A. Documents where user.contact has any field

B. Documents where user.contact.phone exists

C. Documents where user.contact.email exists

D. All documents in the collection

Solution

1. Step 1: Understand $exists operator with nested fields

   The query checks if the nested field "user.contact.email" exists in documents.

2. Step 2: Identify which documents have that nested field

   Only the first two documents have "user.contact.email"; the third has "user.contact.phone" instead.

3. Final Answer:

   Documents where user.contact.email exists -> Option C

4. Quick Check:

   $exists true filters documents with that nested field [OK]

Hint: Use $exists to check nested field presence [OK]

Common Mistakes:

• Assuming $exists checks parent fields
• Confusing email and phone fields
• Expecting all documents to match

4. You wrote this query to find documents where profile.address.zipcode is "12345":

db.users.find({ profile.address.zipcode: "12345" })

But it gives a syntax error. What is the fix?

medium

A. Use quotes around the nested field: { "profile.address.zipcode": "12345" }

B. Replace dots with underscores: { profile_address_zipcode: "12345" }

C. Use double equals: { "profile.address.zipcode" == "12345" }

D. Remove the nested field and query only { zipcode: "12345" }

Solution

1. Step 1: Identify syntax error cause

   MongoDB requires string keys with dot notation quoted in queries to avoid syntax errors.

2. Step 2: Correct query syntax

   Wrap the nested field path in quotes: { "profile.address.zipcode": "12345" } fixes the syntax error.

3. Final Answer:

   Use quotes around the nested field: { "profile.address.zipcode": "12345" } -> Option A

4. Quick Check:

   Quotes fix dot notation syntax errors [OK]

Hint: Always quote nested field keys in queries [OK]

Common Mistakes:

• Not quoting nested field keys
• Using == instead of colon
• Replacing dots with underscores incorrectly

5. You have documents with deeply nested fields like settings.preferences.notifications.email.enabled. How would you write a MongoDB query to find all documents where email notifications are enabled (true), regardless of nesting depth?

hard

A. { "settings.preferences.notifications.email.enabled": true }

B. { settings: { preferences: { notifications: { email: { enabled: true } } } } }

C. { "email.enabled": true }

D. { "settings.preferences.notifications.email.enabled": { $eq: "true" } }

Solution

1. Step 1: Use dot notation string to access deeply nested field

   MongoDB queries use dot notation strings to reach any depth, so "settings.preferences.notifications.email.enabled" is correct.

2. Step 2: Match boolean value correctly

   Use true (boolean) without quotes to match enabled field, so { "settings.preferences.notifications.email.enabled": true } is correct.

3. Final Answer:

   { "settings.preferences.notifications.email.enabled": true } -> Option A

4. Quick Check:

   Dot notation + boolean value = correct query [OK]

Hint: Use full dot path with boolean true (no quotes) [OK]

Common Mistakes:

• Using nested objects instead of dot notation
• Quoting boolean true as string
• Using partial nested paths