Query variables in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this GraphQL query with variables?

Given the following GraphQL query and variables, what will be the value of user.name in the response?

query GetUser($id: ID!) {
  user(id: $id) {
    name
  }
}

Variables:

{"id": "42"}

Assume the user with ID "42" has the name "Alice".

GraphQL

query GetUser($id: ID!) {
  user(id: $id) {
    name
  }
}

A {"errors": [{"message": "Variable '$id' not provided"}]}

B {"data": {"user": {"name": "Alice"}}}

C {"data": {"user": {"name": "42"}}}

D {"data": {"user": null}}

💡 Hint

Variables replace the placeholders in the query. The user with ID "42" is named "Alice".

The variable $id is set to "42", so the query fetches the user with ID "42". The response returns the user's name "Alice".

📝 Syntax

intermediate

Which option correctly declares a required variable in a GraphQL query?

Choose the correct syntax to declare a required variable $limit of type Int in a GraphQL query.

A query GetItems($limit: Int!) { items(limit: $limit) { id } }

B query GetItems($limit: Int) { items(limit: $limit) { id } }

C query GetItems($limit Int!) { items(limit: $limit) { id } }

D query GetItems(limit: Int!) { items(limit: $limit) { id } }

💡 Hint

Required variables use an exclamation mark ! after the type and must be declared with a $ prefix.

Option A correctly declares $limit as a required Int variable. Option A is optional (no !). Option A misses a colon. Option A misses the $ before limit.

❓ optimization

advanced

How can query variables improve GraphQL query performance?

Which of the following best explains how using query variables can improve performance in GraphQL?

A Variables encrypt the query data, improving security and speed.

B Variables reduce the size of the response by compressing data automatically.

C Variables enable the client to send multiple queries in one request, reducing network calls.

D Variables allow the server to cache the query plan and reuse it with different inputs, reducing parsing and validation time.

💡 Hint

Think about how the server handles queries with the same structure but different inputs.

Using variables lets the server parse and validate the query once, then reuse the execution plan with different variable values. This saves processing time and improves performance.

🔧 Debug

advanced

What error occurs if a required variable is missing in a GraphQL request?

Given this query:

query GetPost($postId: ID!) {
  post(id: $postId) {
    title
  }
}

If the request is sent without providing postId in variables, what error will the server return?

A {"errors": [{"message": "Field 'post' not found."}]}

B {"data": {"post": null}}

C {"errors": [{"message": "Variable '$postId' of required type 'ID!' was not provided."}]}

D {"data": {}}

💡 Hint

Required variables must be provided or the server returns an error.

The server returns an error message indicating the required variable $postId was not provided, as it is mandatory.

🧠 Conceptual

expert

Why use query variables instead of hardcoding values in GraphQL queries?

Which of the following is the best reason to use query variables rather than hardcoding values directly in GraphQL queries?

A Variables allow reuse of the same query with different inputs without changing the query text, improving maintainability and caching.

B Variables force the server to execute queries faster by parallel processing.

C Variables reduce the size of the query by removing unnecessary fields.

D Variables automatically encrypt sensitive data sent to the server.

💡 Hint

Think about how variables help with query reuse and server caching.

Using variables lets clients send the same query text with different inputs, which helps caching and makes code easier to maintain. The other options are incorrect or unrelated.