Type conversion expressions ($toInt, $toString) in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the $toInt expression do in MongoDB?

It converts a value to an integer type. For example, a string like "123" becomes the number 123.

beginner

How does $toString work in MongoDB?

It converts a value to a string type. For example, the number 456 becomes the string "456".

intermediate

Why would you use $toInt in a MongoDB aggregation pipeline?

To make sure values are treated as numbers for calculations or comparisons, especially if they are stored as strings.

intermediate

What happens if $toInt tries to convert a non-numeric string?

It results in an error or null depending on the context, because the string cannot be converted to a number.

beginner

Give an example of using $toString in a MongoDB aggregation.

Example: { $toString: "$age" } converts the numeric field age to a string.

What type does $toInt convert a value into?

A String

B Array

C Boolean

D Integer

$toInt converts values to integers.

Which expression converts a number to a string in MongoDB?

A $toString

B $toInt

C $toBool

D $toArray

$toString converts values to strings.

What will { $toInt: "123" } return?

A 123

B null

C Error

D "123"

The string "123" converts to the integer 123.

If $toInt tries to convert "abc", what happens?

A Returns 0

B Returns "abc"

C Error or null

D Returns true

Non-numeric strings cause an error or null when converted to int.

Why use $toString in aggregation?

A To perform math operations

B To convert numbers to strings for display or concatenation

C To filter documents

D To sort documents

$toString helps convert numbers to strings for display or joining text.

Explain how and why you would use $toInt and $toString in a MongoDB aggregation pipeline.

Think about data types and what operations need numbers or strings.

What are possible issues when converting types with $toInt and how can you handle them?

Consider what happens if the data is not in the expected format.