In and not-in queries in Firebase - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

What is the result of this Firestore 'in' query?

Consider a Firestore collection 'products' with documents having a field 'category'. What will this query return?

db.collection('products').where('category', 'in', ['electronics', 'books']).get()

Choose the correct description of the query result.

A Documents where 'category' is not 'electronics' or 'books'.

B Documents where 'category' is both 'electronics' and 'books' at the same time.

C Documents where 'category' is exactly the array ['electronics', 'books'].

D Documents where 'category' is either 'electronics' or 'books'.

💡 Hint

Think about how 'in' works as a filter for multiple possible values.

The 'in' query returns documents where the field matches any value in the given array. It does not require the field to match all values or be an array itself.

❓ service_behavior

intermediate

What happens if you use 'not-in' with more than 10 values in Firestore?

Firestore limits the number of values in 'in' and 'not-in' queries. What will happen if you run this query?

db.collection('users').where('status', 'not-in', ['active', 'pending', 'banned', 'deleted', 'archived', 'new', 'verified', 'suspended', 'guest', 'admin', 'moderator']).get()

Choose the correct outcome.

A The query will fail with an error about too many values in 'not-in'.

B The query will return all documents except those with the listed statuses.

C The query will ignore extra values and only use the first 10.

D The query will return no documents because 'not-in' does not support arrays.

💡 Hint

Check Firestore's documented limits on 'in' and 'not-in' queries.

Firestore limits 'in' and 'not-in' queries to a maximum of 10 values. Exceeding this causes an error.

❓ Architecture

advanced

How to efficiently query documents excluding multiple values in Firestore?

You want to get all documents from 'orders' collection where 'status' is not any of ['cancelled', 'returned', 'failed']. Which approach is best to handle this in Firestore given its query limitations?

A Add a boolean field 'isValid' and query where 'isValid' is true.

B Run multiple queries for each status and merge results client-side.

C Use a 'not-in' query with the array ['cancelled', 'returned', 'failed'].

D Use a 'where' query with '!=' operator for each status combined with 'or'.

💡 Hint

Consider Firestore's support for 'not-in' with up to 10 values.

Firestore supports 'not-in' queries with up to 10 values, so using 'not-in' with these three statuses is efficient and simple.

❓ security

advanced

What security risk arises from using 'in' queries with user input in Firestore?

If you allow users to provide an array of values for an 'in' query on a Firestore collection, what is a potential security concern?

A The 'in' query exposes all documents regardless of security rules.

B Users might query too many values causing denial of service by exhausting Firestore limits.

C Users can modify documents directly through the 'in' query.

D There is no security risk because Firestore automatically filters queries.

💡 Hint

Think about how query complexity affects backend resources.

Allowing users to input large arrays for 'in' queries can cause performance issues or errors due to Firestore's limits, potentially leading to denial of service.

🧠 Conceptual

expert

Why can't Firestore 'not-in' queries be combined with '!=' filters on the same field?

Firestore does not allow combining 'not-in' and '!=' filters on the same field in a single query. Why is this restriction in place?

A Because both filters exclude values and combining them creates conflicting conditions Firestore cannot resolve.

B Because Firestore only supports one filter per field in any query.

C Because '!=' filters are deprecated and replaced by 'not-in' queries.

D Because combining these filters would return all documents, making the query pointless.

💡 Hint

Firestore does not allow multiple filters on the same field.

Firestore only supports one filter per field in any query. You cannot combine multiple filters like 'not-in' and '!=' on the same field.