String expressions ($concat, $toUpper, $toLower) in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the $concat expression do in MongoDB?

It joins two or more strings together into one string.

beginner

How does $toUpper transform a string in MongoDB?

It changes all letters in the string to uppercase letters.

beginner

What is the purpose of $toLower in MongoDB string expressions?

It converts all letters in a string to lowercase letters.

intermediate

Write a MongoDB expression to combine first name and last name with a space in between.

Use { $concat: ["$firstName", " ", "$lastName"] } to join firstName and lastName with a space.

intermediate

How can you convert a user's name to uppercase and then concatenate with a greeting in MongoDB?

Use { $concat: ["Hello, ", { $toUpper: "$name" }] } to greet with uppercase name.

Which MongoDB expression joins multiple strings into one?

A $toUpper

B $toLower

C $concat

D $split

$concat joins strings; $toUpper and $toLower change case; $split breaks strings apart.

What does $toUpper do to the string "hello"?

A "HELLO"

B "hello"

C "Hello"

D "hElLo"

$toUpper converts all letters to uppercase.

How would you convert "WORLD" to lowercase in MongoDB?

A { $toLower: "WORLD" }

B { $toUpper: "WORLD" }

C { $concat: ["W", "O", "R", "L", "D"] }

D { $substr: ["WORLD", 0, 5] }

$toLower changes all letters to lowercase.

Which expression correctly joins firstName and lastName with a space?

A { $concat: ["$firstName", "$lastName"] }

B { $concat: ["$firstName", " ", "$lastName"] }

C { $toUpper: ["$firstName", " ", "$lastName"] }

D { $toLower: ["$firstName", " ", "$lastName"] }

You need to add a space string " " between the two fields in $concat.

What will this expression return? { $concat: ["Hi, ", { $toUpper: "$user" }] } if user is "anna"?

A "Hi, anna"

B "hi, ANNA"

C "ANNA"

D "Hi, ANNA"

It concatenates "Hi, " with the uppercase version of "anna", which is "ANNA".

Explain how to use $concat, $toUpper, and $toLower in MongoDB to format a full name.

Think about joining first and last names and changing case.

Describe a real-life example where $concat and $toUpper could be used together in a MongoDB query.

Imagine saying hello to a user with their name in capital letters.