First GraphQL query - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this GraphQL query?

Given a GraphQL schema with a Book type having fields title and author, and a query:

{ books { title author } }

What is the expected output if the data contains two books: "1984" by "George Orwell" and "Brave New World" by "Aldous Huxley"?

GraphQL

{ books { title author } }

A {"data":{"books":[{"author":"George Orwell"},{"author":"Aldous Huxley"}]}}

B {"data":{"books":[{"title":"1984"},{"title":"Brave New World"}]}}

C {"errors":[{"message":"Field 'author' not found"}]}

D {"data":{"books":[{"title":"1984","author":"George Orwell"},{"title":"Brave New World","author":"Aldous Huxley"}]}}

💡 Hint

Remember that the query requests both title and author fields for each book.

The query asks for both title and author of each book. The data contains two books with those fields, so the output includes both fields for both books.

🧠 Conceptual

intermediate

Which statement best describes a GraphQL query?

Choose the statement that correctly describes what a GraphQL query does.

A It sends a full database dump from the server to the client.

B It requests specific fields from the server, returning only the requested data.

C It updates data on the server without returning any data.

D It automatically generates a user interface based on the schema.

💡 Hint

Think about how GraphQL differs from REST in terms of data fetching.

GraphQL queries specify exactly which fields to fetch, so the server returns only that data, making data fetching efficient.

📝 Syntax

advanced

Identify the syntax error in this GraphQL query

Find the syntax error in the following GraphQL query:

{ books { title author } 

GraphQL

{ books { title author } 

A The query must start with the keyword 'query'.

B Field names must be quoted with double quotes.

C Missing closing brace '}' at the end of the query.

D The fields must be separated by commas.

💡 Hint

Check if all braces are properly closed.

The query is missing the final closing brace '}', which is required to close the query block.

❓ optimization

advanced

How to reduce data transfer in a GraphQL query?

You want to fetch only the book titles from a large list of books to reduce data transfer. Which query is best?

A { books { title } }

B { books { title author } }

C { books }

D { books { id } }

💡 Hint

Only request the fields you need.

Requesting only the title field reduces the amount of data sent compared to requesting more fields.

🔧 Debug

expert

Why does this GraphQL query return an error?

Given the schema where Book has fields title and author, why does this query return an error?

{ books { title publisher } }

GraphQL

{ books { title publisher } }

A The field 'publisher' does not exist in the 'Book' type.

B The query is missing a root operation type like 'query'.

C The field 'title' must be nested inside 'author'.

D GraphQL queries cannot request more than one field.

💡 Hint

Check if all requested fields exist in the schema.

The error occurs because 'publisher' is not defined in the 'Book' type, so the server rejects the query.

Practice

1. What does a basic GraphQL query do?

easy

A. It asks for specific data by listing fields inside curly braces.

B. It updates data in the database.

C. It deletes data from the server.

D. It creates a new database schema.

Solution

1. Step 1: Understand GraphQL query purpose

   A GraphQL query is designed to request specific data from a server.

2. Step 2: Identify query syntax

   The query lists the fields wanted inside curly braces to specify what data to fetch.

3. Final Answer:

   It asks for specific data by listing fields inside curly braces. -> Option A

4. Quick Check:

   GraphQL query = request data [OK]

Hint: Remember: queries fetch data by listing fields [OK]

Common Mistakes:

• Confusing queries with mutations
• Thinking queries modify data
• Mixing query syntax with SQL

2. Which of the following is the correct syntax for a simple GraphQL query to get a user's name?

easy

A. query { user { name } }

B. query user { name }

C. { user name }

D. query user name { }

Solution

1. Step 1: Review GraphQL query structure

   A query starts with the keyword 'query' (optional), followed by curly braces enclosing the fields.

2. Step 2: Check each option's syntax

   query { user { name } } correctly uses 'query' and nested braces for user and name fields.

3. Final Answer:

   query { user { name } } -> Option A

4. Quick Check:

   Correct braces and field nesting = query { user { name } } [OK]

Hint: Use nested braces for nested fields [OK]

Common Mistakes:

• Missing curly braces
• Incorrect field nesting
• Wrong keyword placement

3. Given this GraphQL query:

query { book { title author } }

What data will the server return?

medium

A. SyntaxError: Missing fields

B. { "data": { "book": "title author" } }

C. { "book": { "title": "string", "author": "string" } }

D. { "data": { "book": { "title": "string", "author": "string" } } }

Solution

1. Step 1: Understand GraphQL response format

   GraphQL returns data inside a 'data' object matching the query structure.

2. Step 2: Match query fields to response

   The query asks for 'book' with 'title' and 'author', so response includes these nested fields.

3. Final Answer:

   { "data": { "book": { "title": "string", "author": "string" } } } -> Option D

4. Quick Check:

   Response matches query structure [OK]

Hint: Response wraps requested fields inside 'data' object [OK]

Common Mistakes:

• Omitting 'data' wrapper in response
• Returning fields as a string
• Confusing syntax error with valid query

4. Identify the error in this GraphQL query:

query { user { id name 

medium

A. Fields 'id' and 'name' are invalid.

B. Incorrect keyword 'query' used.

C. Missing closing curly braces for 'user' and 'query'.

D. Query should not have nested fields.

Solution

1. Step 1: Check query syntax completeness

   The query opens braces for 'user' and 'query' but does not close them.

2. Step 2: Confirm correct use of keywords and fields

   'query' keyword is correct; 'id' and 'name' are valid fields; nested fields are allowed.

3. Final Answer:

   Missing closing curly braces for 'user' and 'query'. -> Option C

4. Quick Check:

   Unclosed braces cause syntax error [OK]

Hint: Count opening and closing braces carefully [OK]

Common Mistakes:

• Forgetting to close all braces
• Assuming keywords are wrong
• Thinking nested fields are invalid

5. You want to fetch a list of users with their id and name using GraphQL. Which query correctly does this assuming the server has a 'users' field returning a list?

hard

A. query { users: id, name }

B. query { users { id name } }

C. query { user { id name } }

D. query users { id name }

Solution

1. Step 1: Identify the correct root field for multiple users

   The server field for multiple users is 'users', not 'user'.

2. Step 2: Check query syntax for nested fields

   query { users { id name } } correctly queries 'users' with nested 'id' and 'name' fields inside braces.

3. Final Answer:

   query { users { id name } } -> Option B

4. Quick Check:

   Correct root field and nested fields = query { users { id name } } [OK]

Hint: Use plural field for lists, nest fields inside braces [OK]

Common Mistakes:

• Using singular 'user' for list data
• Incorrect field alias syntax
• Omitting braces for nested fields