String and number types in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What data type is used to store text in MongoDB?

The String data type is used to store text in MongoDB. It stores sequences of characters like words or sentences.

beginner

Name two number types in MongoDB and their difference.

MongoDB uses int for 32-bit integers and double for 64-bit floating-point numbers.
Int stores whole numbers, while double can store decimals.

beginner

How does MongoDB store a number with decimals?

MongoDB stores numbers with decimals using the double type, which is a 64-bit floating-point number.

intermediate

What happens if you store a large whole number in MongoDB that exceeds 32-bit integer range?

If the number is too large for 32-bit int, MongoDB stores it as a long (64-bit integer) or double depending on the value.

intermediate

Why is it important to choose the correct number type in MongoDB?

Choosing the correct number type helps save space and ensures accurate calculations. For example, using int for whole numbers is efficient, while double is needed for decimals.

Which MongoDB data type is best for storing a person's name?

A String

B int

C double

D boolean

Names are text, so the String type is the correct choice.

What type does MongoDB use to store a number like 42?

A double

B boolean

C int

D string

42 is a whole number that fits in 32-bit int, so MongoDB stores it as int.

Which type should you use to store the number 3.14 in MongoDB?

A double

B int

C string

D long

3.14 has decimals, so it must be stored as a double.

If a number is too big for int, MongoDB stores it as:

A boolean

B long or double

C string

D array

Large numbers are stored as long (64-bit int) or double depending on the value.

Which MongoDB type is NOT used for numbers?

A long

B double

C int

D string

String is for text, not numbers.

Explain the difference between String and number types in MongoDB and when to use each.

Think about what kind of data you want to save: words or numbers.

Describe how MongoDB handles large numbers that don't fit in 32-bit integers.

Consider the size limits of int and alternatives.

Practice

1. Which of the following is the correct way to store a string value in a MongoDB document?

easy

A. Use single quotes only, like 'Hello'

B. Write the text without quotes, like Hello

C. Write the text as a number, like 123

D. Use quotes around the text, like "Hello"

Solution

1. Step 1: Understand string representation in MongoDB

   Strings must be enclosed in quotes to be recognized as text.

2. Step 2: Identify correct syntax for strings

   Double quotes or single quotes can be used, but quotes are necessary around text.

3. Final Answer:

   Use quotes around the text, like "Hello" -> Option D

4. Quick Check:

   Strings need quotes = C [OK]

Hint: Strings always need quotes around text in MongoDB [OK]

Common Mistakes:

• Writing text without quotes causes errors
• Confusing numbers with strings
• Using numbers when text is needed

2. Which of the following is the correct way to store the number 42 in a MongoDB document?

easy

A. Write it as '42' with single quotes

B. Write it as "42" with quotes

C. Write it as 42 without quotes

D. Write it as forty-two without quotes

Solution

1. Step 1: Understand number representation in MongoDB

   Numbers are stored without quotes to be recognized as numeric values.

2. Step 2: Identify correct syntax for numbers

   Writing numbers without quotes stores them as numeric types, not strings.

3. Final Answer:

   Write it as 42 without quotes -> Option C

4. Quick Check:

   Numbers have no quotes = A [OK]

Hint: Numbers never have quotes in MongoDB documents [OK]

Common Mistakes:

• Putting numbers inside quotes makes them strings
• Using words instead of digits for numbers
• Mixing string and number types

3. What will be the output of this MongoDB query?

db.products.find({ price: 100 })

Assuming the collection has documents:

{ "name": "Pen", "price": 100 }
{ "name": "Book", "price": "100" }

medium

A. Returns only the document where price is number 100

B. Returns both documents because price matches 100

C. Returns only the document where price is string "100"

D. Returns no documents because of type mismatch

Solution

1. Step 1: Understand MongoDB type matching in queries

   MongoDB matches both value and type when querying, so number 100 matches only number 100.

2. Step 2: Analyze the documents

   Document with price as number 100 matches; document with price as string "100" does not.

3. Final Answer:

   Returns only the document where price is number 100 -> Option A

4. Quick Check:

   Query matches value and type = B [OK]

Hint: MongoDB matches type and value in queries [OK]

Common Mistakes:

• Assuming string and number values match
• Ignoring type differences in queries
• Expecting all similar values to match

4. You wrote this MongoDB insert command:

db.users.insertOne({ "age": "30" })

But you want age stored as a number. What is wrong?

medium

A. The insertOne command syntax is incorrect

B. Age is stored as a string because of quotes around 30

C. The field name should be "Age" with capital A

D. Age is stored as a number but should be a string

Solution

1. Step 1: Check the value type in the insert command

   Quotes around 30 make it a string, not a number.

2. Step 2: Understand how to store numbers

   To store as number, write 30 without quotes.

3. Final Answer:

   Age is stored as a string because of quotes around 30 -> Option B

4. Quick Check:

   Quotes make value string = D [OK]

Hint: Remove quotes to store numbers, add quotes for strings [OK]

Common Mistakes:

• Thinking quotes don't affect type
• Changing field name unnecessarily
• Assuming syntax error without checking value type

5. You have a collection with documents:

{ "item": "apple", "quantity": "10" }
{ "item": "banana", "quantity": 10 }

You want to find all documents where quantity is greater than 5. Which query works correctly?

hard

A. db.collection.find({ quantity: { $gt: NumberInt(5) } })

B. db.collection.find({ quantity: { $gt: "5" } })

C. db.collection.find({ quantity: { $gt: 5 } })

D. db.collection.find({ quantity: { $gt: 5 } }).toArray()

Solution

1. Step 1: Understand type comparison in MongoDB queries

   MongoDB compares values and types; string "10" is not greater than number 5.

2. Step 2: Use NumberInt to ensure numeric comparison

   Using NumberInt(5) ensures the query compares numbers, matching numeric quantity fields.

3. Final Answer:

   db.collection.find({ quantity: { $gt: NumberInt(5) } }) -> Option A

4. Quick Check:

   Use numeric type for numeric comparison = A [OK]

Hint: Use numeric types in queries to compare numbers correctly [OK]

Common Mistakes:

• Comparing strings with numbers directly
• Using quotes around numbers in queries
• Assuming all quantity fields are same type