How MongoDB stores data as documents - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert a document into the collection.

MongoDB

db.collection.insertOne({ name: "Alice", age: [1] })

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

Aage

B25

C"25"

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Putting numbers inside quotes makes them strings.

Using undefined variables instead of values.

The age field should be a number, so 25 without quotes is correct.

2fill in blank

medium

Complete the code to find all documents where age is greater than 20.

MongoDB

db.collection.find({ age: { [1]: 20 } })

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

A$lt

B$ne

C$eq

D$gt

Attempts:

3 left

💡 Hint

Common Mistakes

Using $lt which means less than.

Using $eq which means equal.

The operator $gt means 'greater than'.

3fill in blank

hard

Fix the error in the query to find documents with name 'Bob'.

MongoDB

db.collection.find({ name: [1] })

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

A"Bob"

B{Bob}

C'Bob'

DBob

Attempts:

3 left

💡 Hint

Common Mistakes

Not using quotes around string values.

Using single quotes which may cause errors in some shells.

String values in MongoDB queries must be in double quotes.

4fill in blank

hard

Fill both blanks to create a document with a nested address field.

MongoDB

db.collection.insertOne({ name: "Eve", address: { [1]: "123 Main St", [2]: "NY" } })

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

Astreet

Bcity

Cstate

Dzip

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up city and state fields.

Using invalid field names.

The nested document has fields 'street' and 'state' for the address.

5fill in blank

hard

Fill all three blanks to query documents where age is less than 30 and city is 'LA'.

MongoDB

db.collection.find({ [1]: { [2]: 30 }, city: [3] })

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

Aage

B$lt

C"LA"

Dcity

Attempts:

3 left

💡 Hint

Common Mistakes

Using $gt instead of $lt.

Not quoting string values.

Mixing up field names.

The query filters documents where age is less than 30 and city equals 'LA'.

Practice

1. What is the basic unit of data storage in MongoDB?

easy

A. A document

B. A table

C. A row

D. A column

Solution

1. Step 1: Understand MongoDB data structure

   MongoDB stores data as documents, not tables or rows like traditional databases.

2. Step 2: Identify the correct data unit

   The document is the flexible data unit that holds fields and values in MongoDB.

3. Final Answer:

   A document -> Option A

4. Quick Check:

   MongoDB data unit = document [OK]

Hint: Remember: MongoDB uses documents, not tables or rows [OK]

Common Mistakes:

• Confusing documents with tables from SQL
• Thinking rows or columns are used in MongoDB
• Assuming collections are the basic unit

2. Which of the following is the correct way to represent a MongoDB document with a field name and value Alice?

easy

A. [ 'name': 'Alice' ]

B. { 'name' = 'Alice' }

C. { name: 'Alice' }

D. ( name: 'Alice' )

Solution

1. Step 1: Recall MongoDB document syntax

   MongoDB documents use JSON-like syntax with curly braces and colon to assign values.

2. Step 2: Check each option's syntax

   { name: 'Alice' } uses correct JSON-like syntax: { name: 'Alice' }. Others use invalid symbols or brackets.

3. Final Answer:

   { name: 'Alice' } -> Option C

4. Quick Check:

   Correct MongoDB document = JSON-like with colons [OK]

Hint: Use curly braces and colons for fields in MongoDB documents [OK]

Common Mistakes:

• Using equal signs instead of colons
• Using square or round brackets instead of curly braces
• Putting field names in quotes incorrectly

3. Given the MongoDB document: { name: 'Bob', age: 30, hobbies: ['reading', 'swimming'] }, what is the value of the hobbies field?

medium

A. A string 'reading, swimming'

B. A nested document with keys 'reading' and 'swimming'

C. A number 2

D. An array with 'reading' and 'swimming'

Solution

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

   The hobbies field is shown with square brackets, which means it is an array.

2. Step 2: Understand array contents

   The array contains two string elements: 'reading' and 'swimming'.

3. Final Answer:

   An array with 'reading' and 'swimming' -> Option D

4. Quick Check:

   Square brackets mean array = An array with 'reading' and 'swimming' [OK]

Hint: Square brackets [] mean array in MongoDB documents [OK]

Common Mistakes:

• Thinking it's a string instead of an array
• Confusing arrays with nested documents
• Assuming the value is a count of items

4. Identify the error in this MongoDB document: { 'title': 'Book', pages: 250, author: 'John Doe' }

medium

A. This document is valid and has no error

B. Mixing quoted and unquoted field names is invalid

C. Values must be numbers only

D. Field names must all be unquoted

Solution

1. Step 1: Check field name quoting rules

   MongoDB allows field names to be quoted or unquoted as long as they are valid strings.

2. Step 2: Verify document validity

   Mixing quoted and unquoted field names is allowed; values are correctly typed.

3. Final Answer:

   This document is valid and has no error -> Option A

4. Quick Check:

   Quoted or unquoted field names both valid [OK]

Hint: MongoDB allows mixed quoted/unquoted field names [OK]

Common Mistakes:

• Thinking all field names must be quoted
• Assuming mixing quotes causes error
• Believing values must be only numbers

5. You want to store a user's profile with name, age, and a list of addresses (each with street and city) in MongoDB. Which document structure correctly represents this?

hard

A. { name: 'Eva', age: 28, addresses: '1st Ave, NY; 2nd St, LA' }

B. { name: 'Eva', age: 28, addresses: [{ street: '1st Ave', city: 'NY' }, { street: '2nd St', city: 'LA' }] }

C. { name: 'Eva', age: 28, addresses: { street: '1st Ave', city: 'NY' }, { street: '2nd St', city: 'LA' } }

D. [ name: 'Eva', age: 28, addresses: [{ street: '1st Ave', city: 'NY' }] ]

Solution

1. Step 1: Understand nested documents and arrays

   Addresses is a list (array) of objects (documents), each with street and city fields.

2. Step 2: Check each option's structure

   { name: 'Eva', age: 28, addresses: [{ street: '1st Ave', city: 'NY' }, { street: '2nd St', city: 'LA' }] } correctly uses an array of documents inside the addresses field. Others use strings, invalid syntax, or wrong brackets.

3. Final Answer:

   { name: 'Eva', age: 28, addresses: [{ street: '1st Ave', city: 'NY' }, { street: '2nd St', city: 'LA' }] } -> Option B

4. Quick Check:

   Array of nested documents = { name: 'Eva', age: 28, addresses: [{ street: '1st Ave', city: 'NY' }, { street: '2nd St', city: 'LA' }] } [OK]

Hint: Use array of documents for multiple nested objects [OK]

Common Mistakes:

• Storing nested data as a plain string
• Using invalid JSON syntax with multiple objects outside array
• Using square brackets for entire document instead of curly braces