Persisted queries in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the result of executing a persisted query with a missing hash?

Consider a GraphQL server that uses persisted queries identified by SHA-256 hashes. If a client sends a request with a hash that does not match any stored query, what will the server respond with?

A The server ignores the hash and executes the query text sent by the client.

B The server executes a default fallback query instead.

C The server returns an error indicating the query was not found.

D The server caches the new query under the given hash automatically.

💡 Hint

Think about what happens when the server cannot find a query matching the client's hash.

Persisted queries rely on the server having the query stored under the given hash. If the hash is unknown, the server cannot execute the query and returns an error.

🧠 Conceptual

intermediate

Why use persisted queries in GraphQL?

Which of the following is the main benefit of using persisted queries in GraphQL?

A To reduce the size of requests by sending only query hashes instead of full query text.

B To allow clients to send multiple queries in a single request.

C To enable real-time subscriptions over WebSocket connections.

D To automatically generate schema documentation.

💡 Hint

Think about network efficiency and bandwidth savings.

Persisted queries reduce request size by sending only a small hash instead of the full query text, improving performance especially on slow networks.

📝 Syntax

advanced

Which option correctly shows how to register a persisted query in a GraphQL server?

Given a GraphQL server setup, which snippet correctly registers a persisted query with hash abc123 and query { user { id name } }?

A persistedQueries.set('abc123', '{ user { id name } }');

B persistedQueries.add('{ user { id name } }', 'abc123');

C persistedQueries['abc123'] = '{ user { id name } }';

D persistedQueries.register('{ user { id name } }', 'abc123');

💡 Hint

Consider common JavaScript Map methods for storing key-value pairs.

The set method is used to add a key-value pair to a Map object, where the key is the hash and the value is the query string.

❓ optimization

advanced

How do persisted queries improve caching efficiency?

Which statement best explains how persisted queries help with caching on the server or CDN?

A Persisted queries disable caching to ensure fresh data every time.

B Persisted queries compress the query text to reduce cache size.

C Persisted queries require clients to send full query text, improving cache hits.

D Persisted queries use fixed hashes, allowing caches to store and identify queries by hash instead of varying query text.

💡 Hint

Think about how identical keys help caches recognize repeated requests.

Using a fixed hash as a key means caches can easily identify repeated queries and serve cached responses, improving performance.

🔧 Debug

expert

What error occurs if a client sends a persisted query hash but no query text and the hash is unknown?

A client sends a GraphQL request with only a persisted query hash that the server does not recognize, and no query text. What error will the server produce?

A TimeoutError because the server waits for query text indefinitely.

B PersistedQueryNotFound error indicating the hash is unknown.

C AuthenticationError because the client is unauthorized.

D SyntaxError due to missing query text.

💡 Hint

Consider the server's response when it cannot find the query for the given hash.

The server returns a specific PersistedQueryNotFound error when the hash is unknown and no query text is provided to fallback on.