Query limitations and workarounds in Firebase - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Firestore Query Limitations

Firestore queries have some limitations. Which of the following is NOT a Firestore query limitation?

A You cannot perform a query with multiple inequality filters on different fields.

B You cannot perform a query that combines 'OR' conditions directly.

C You cannot query documents without an index on the queried fields.

D You cannot order query results by a field that is not included in the filters.

💡 Hint

Think about what Firestore allows in ordering and filtering.

Firestore allows ordering by fields even if they are not filtered, but it requires indexes for certain queries. Multiple inequality filters on different fields and direct 'OR' queries are not supported.

❓ Architecture

intermediate

Workaround for Firestore 'OR' Queries

You want to query documents where status is 'active' OR priority is 'high'. Firestore does not support 'OR' queries directly. Which approach correctly implements this?

A Perform two separate queries and merge results in the client.

B Use a single query with multiple inequality filters on both fields.

C Create a composite field combining status and priority and query on it.

D Use Firestore's 'array-contains-any' operator on both fields.

💡 Hint

Consider how Firestore handles multiple queries and client-side merging.

Firestore does not support 'OR' queries directly. The common workaround is to run multiple queries and merge results on the client side.

❓ Configuration

advanced

Index Configuration for Complex Queries

You have a Firestore query filtering by category and ordering by timestamp. The query fails due to missing index. Which index configuration is required?

Firebase

collection: products
fields:
  - fieldPath: category
    order: ASCENDING
  - fieldPath: timestamp
    order: DESCENDING

A An index on category ascending and timestamp descending.

B An index on timestamp ascending only.

C An index on category descending and timestamp ascending.

D No index needed; Firestore supports this query by default.

💡 Hint

Check the order directions in the query and index.

Firestore requires a composite index matching the filter and order directions exactly.

❓ service_behavior

advanced

Behavior of Firestore Queries with Inequality Filters

What happens if you try to run a Firestore query with inequality filters on two different fields, for example age > 20 and score < 50?

A The query runs successfully and returns matching documents.

B The query fails with an error about multiple inequality filters.

C The query ignores one of the inequality filters and runs.

D The query runs but returns no documents.

💡 Hint

Recall Firestore's rules on inequality filters.

Firestore does not allow inequality filters on more than one field in a single query.

❓ security

expert

Securing Queries with Firestore Rules and Query Limitations

You want to secure a Firestore collection so users can only read documents where ownerId equals their user ID. You write a security rule using request.auth.uid == resource.data.ownerId. Which query limitation must you consider to ensure the query passes the security rules?

A The query can omit filtering on <code>ownerId</code> because rules handle security.

B The query must order by <code>ownerId</code> but not filter on it.

C The query must include a filter on <code>ownerId</code> equal to the user's ID.

D The query must use a composite index on <code>ownerId</code> and <code>timestamp</code>.

💡 Hint

Think about how Firestore security rules interact with queries.

Firestore requires queries to include filters matching security rules to avoid returning unauthorized data.