String and number types in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Find documents with numeric string values

Given a collection products where the field price is stored as a string, which query returns all documents where price is a string representing a number greater than 100?

MongoDB

db.products.find({ price: { $gt: "100" } })

A db.products.find({ price: { $gte: "100" } })

B db.products.find({ price: { $gt: "100" } })

C db.products.find({ price: { $gte: 100 } })

D db.products.find({ price: { $gt: 100 } })

💡 Hint

Remember that comparing strings with $gt compares lexicographically.

Since price is stored as a string, the query must compare strings. Using $gt: "100" compares string values lexicographically, which matches strings greater than "100".

📝 Syntax

intermediate

Identify the correct syntax for storing a number as a string

Which of the following MongoDB insert commands correctly stores the field age as a string with value "30"?

A db.users.insertOne({ name: "Alice", age: Number("30") })

B db.users.insertOne({ name: "Alice", age: 30 })

C db.users.insertOne({ name: "Alice", age: "30" })

D db.users.insertOne({ name: "Alice", age: String(30) })

💡 Hint

Strings must be enclosed in quotes.

To store age as a string, the value must be enclosed in quotes. Option C uses "30" which is a string literal.

🧠 Conceptual

advanced

Understanding BSON types for numbers and strings

In MongoDB, which BSON type is used to store a 64-bit integer number?

A Int64 (Long)

B Double

C String

D Decimal128

💡 Hint

Think about the size and precision of the number type.

MongoDB uses the Int64 (also called Long) BSON type to store 64-bit integer numbers exactly.

🔧 Debug

advanced

Why does this query not return expected numeric results?

Consider the collection sales where amount is stored as a string. The query db.sales.find({ amount: { $gt: 100 } }) returns no documents. Why?

MongoDB

db.sales.find({ amount: { $gt: 100 } })

A Because <code>amount</code> is a string, comparing with number 100 fails to match any document.

B Because <code>$gt</code> operator only works with numbers, not strings.

C Because the query syntax is invalid and causes an error.

D Because the collection <code>sales</code> is empty.

💡 Hint

Check the data type of the field and the query value.

MongoDB does not convert types automatically in queries. Comparing a string field with a number value does not match any documents.

❓ optimization

expert

Optimizing queries on numeric strings

You have a collection orders where the field quantity is stored as a string. You want to efficiently find all orders with quantity greater than 50. Which approach is best?

A Use a regex query to match quantities greater than 50 as strings.

B Convert <code>quantity</code> to number in each query using aggregation and filter after conversion.

C Use <code>db.orders.find({ quantity: { $gt: "50" } })</code> and create an index on <code>quantity</code>.

D Update the collection to store <code>quantity</code> as a number and create an index on it.

💡 Hint

Think about data types and indexing for performance.

Storing numeric data as strings prevents efficient numeric queries and indexing. Converting the field to a numeric type and indexing it improves query speed and correctness.