Comparison operators (==, <, >, >=, <=) in Firebase - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

Firebase Realtime Database: Query with < operator

You want to retrieve all users whose age is less than 30 from your Firebase Realtime Database. Which query will correctly return these users?

Firebase

firebase.database().ref('users').orderByChild('age').<operator>(30).once('value').then(snapshot => { /* handle data */ });

A firebase.database().ref('users').orderByChild('age').endBefore(30).once('value')

B firebase.database().ref('users').orderByChild('age').startAt(30).once('value')

C firebase.database().ref('users').orderByChild('age').equalTo(30).once('value')

D firebase.database().ref('users').orderByChild('age').endAt(29).once('value')

💡 Hint

Think about which method limits results to values less than a given number.

In Firebase Realtime Database, endBefore(30) returns all records with 'age' less than 30. startAt(30) returns ages 30 and above. equalTo(30) returns only age 30. endAt(29) returns ages up to 29 inclusive, but 29 is less than 30, so it works similarly for integer ages.

❓ Architecture

intermediate

Firestore: Filtering documents with >= operator

You want to get all orders with a total amount greater than or equal to 100 in Firestore. Which query correctly achieves this?

Firebase

firebase.firestore().collection('orders').where('total', '<operator>', 100).get().then(snapshot => { /* handle data */ });

A firebase.firestore().collection('orders').where('total', '>=', 100).get()

B firebase.firestore().collection('orders').where('total', '>', 100).get()

C firebase.firestore().collection('orders').where('total', '<=', 100).get()

D firebase.firestore().collection('orders').where('total', '==', 100).get()

💡 Hint

Remember that >= means greater than or equal to.

The 'where' clause with '>=' returns documents where 'total' is 100 or more. '>' excludes 100. '<=' and '==' do not match the requirement.

❓ security

advanced

Firestore Security Rules: Using == operator

You want to allow users to read their own profile document only if their user ID matches the document ID. Which security rule condition correctly enforces this?

Firebase

match /users/{userId} { allow read: if <condition>; }

A request.auth.uid == userId

B request.auth.uid < userId

C request.auth.uid != userId

D request.auth.uid >= userId

💡 Hint

Check for exact equality between authenticated user ID and document ID.

The '==' operator checks if the authenticated user's ID matches the document ID exactly, allowing access only to their own data. Other operators do not enforce this correctly.

✅ Best Practice

advanced

Choosing correct comparison operator in Firestore queries

You want to query Firestore for products priced less than or equal to $50. Which operator should you use in the where clause to get all products priced at $50 or less?

Firebase

firebase.firestore().collection('products').where('price', '<operator>', 50).get()

A '<'

B '<='

C '>'

D '=='

💡 Hint

Think about including the price 50 in the results.

The '<=' operator includes all products priced less than or equal to 50. '<' excludes 50. '>' and '==' do not match the requirement.

🧠 Conceptual

expert

Understanding Firebase Realtime Database query behavior with >= and == operators

Consider this Firebase Realtime Database query to find users with age greater than or equal to 21: firebase.database().ref('users').orderByChild('age').startAt(21).once('value') What will be the difference in results if you replace startAt(21) with equalTo(21)?

A Both return users aged 21 and older

B startAt(21) returns only users aged exactly 21; equalTo(21) returns users aged 21 and older

C startAt(21) returns users aged 21 and older; equalTo(21) returns only users aged exactly 21

D Both return only users aged exactly 21

💡 Hint

Consider how startAt and equalTo filter data differently.

startAt(21) returns all users with age 21 or more. equalTo(21) returns only users whose age is exactly 21.