GraphQL Playground and tools - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary purpose of GraphQL Playground?

GraphQL Playground is a popular tool used by developers. What is its main purpose?

A To convert SQL queries into GraphQL queries

B To deploy GraphQL servers automatically

C To write and test GraphQL queries interactively

D To monitor server CPU and memory usage

💡 Hint

Think about what developers do when they want to try out queries before coding.

GraphQL Playground lets developers write, test, and explore GraphQL queries in an interactive environment.

❓ query_result

intermediate

What is the output of this GraphQL query in Playground?

Given the schema with a user type having fields id and name, what is the output of this query?

{ user(id: 1) { id name } }

GraphQL

{ user(id: 1) { id name } }

A { "data": { "user": { "id": "1", "name": null } } }

B { "data": { "user": null } }

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

D { "data": { "user": { "id": 1, "name": "Alice" } } }

💡 Hint

Assume the user with id 1 exists and has the name 'Alice'.

The query requests user with id 1, returning id and name fields. Since user exists, data is returned with those fields.

📝 Syntax

advanced

Which option contains a syntax error in GraphQL Playground?

Identify the GraphQL query that will cause a syntax error when run in GraphQL Playground.

A { user(id: 4) { id name }

B { user(id: 3) { id name } }

C { user(id: 2) { id name } }

D { user(id: 5) { id name } }

💡 Hint

Look for missing or extra characters that break the query structure.

Option A is missing the closing brace '}', causing a syntax error in the query.

❓ optimization

advanced

Which tool helps optimize GraphQL queries by analyzing performance?

Among these tools, which one is designed to help developers optimize GraphQL queries by analyzing their performance and complexity?

A GraphiQL

B Apollo Engine

C GraphQL Voyager

D GraphQL Playground

💡 Hint

This tool provides metrics and tracing for GraphQL APIs.

Apollo Engine helps monitor and optimize GraphQL queries by providing performance metrics and tracing.

🔧 Debug

expert

What error message will GraphQL Playground show for this query?

Given the schema does not define a posts field on the Query type, what error will GraphQL Playground return for this query?

{ posts { id title } }

GraphQL

{ posts { id title } }

A { "errors": [ { "message": "Cannot query field 'posts' on type 'Query'." } ] }

B { "data": { "posts": [] } }

C { "errors": [ { "message": "Field 'posts' is deprecated." } ] }

D { "data": null }

💡 Hint

Think about what happens when you query a field not defined in the schema.

GraphQL Playground returns an error indicating the field 'posts' does not exist on the Query type.

Practice

1. What is the main purpose of GraphQL Playground?

easy

A. To write and test GraphQL queries easily without extra setup

B. To store large amounts of data permanently

C. To replace SQL databases with a new storage system

D. To create user interfaces for mobile apps

Solution

1. Step 1: Understand GraphQL Playground's role

   GraphQL Playground is a tool designed to help users write and test GraphQL queries interactively.

2. Step 2: Compare options with this role

   Only To write and test GraphQL queries easily without extra setup describes this purpose correctly; others describe unrelated functions.

3. Final Answer:

   To write and test GraphQL queries easily without extra setup -> Option A

4. Quick Check:

   GraphQL Playground = Query testing tool [OK]

Hint: Think: Playground means a place to try things out [OK]

Common Mistakes:

• Confusing Playground with database storage
• Thinking it builds app interfaces
• Assuming it replaces databases

2. Which of the following is the correct way to start a query in GraphQL Playground?

easy

A. SELECT * FROM user

B. query { user { id name } }

C. { user id name }

D. GET user { id, name }

Solution

1. Step 1: Recall GraphQL query syntax

   GraphQL queries start with the keyword query followed by the selection set in braces.

2. Step 2: Check each option's syntax

   query { user { id name } } uses correct GraphQL syntax. Options B and D use SQL or HTTP-like syntax, and C misses the query keyword and braces.

3. Final Answer:

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

4. Quick Check:

   GraphQL queries start with 'query' [OK]

Hint: GraphQL queries start with 'query' keyword and braces [OK]

Common Mistakes:

• Using SQL syntax instead of GraphQL
• Omitting the 'query' keyword
• Missing braces around fields

3. Given this GraphQL query in Playground:

query { book(id: "1") { title author } }

What will the result look like if the book with id "1" has title "GraphQL Guide" and author "Anna"?

medium

A. { "book": { "title": "GraphQL Guide", "author": "Anna" } }

B. { "data": { "book": ["GraphQL Guide", "Anna"] } }

C. { "data": { "book": { "title": "GraphQL Guide", "author": "Anna" } } }

D. { "data": { "book": { "name": "GraphQL Guide", "writer": "Anna" } } }

Solution

1. Step 1: Understand GraphQL response format

   GraphQL responses wrap requested data inside a top-level "data" object matching the query structure.

2. Step 2: Match query fields with response

   The query asks for title and author fields of book. { "data": { "book": { "title": "GraphQL Guide", "author": "Anna" } } } matches this exactly with correct field names and structure.

3. Final Answer:

   { "data": { "book": { "title": "GraphQL Guide", "author": "Anna" } } } -> Option C

4. Quick Check:

   GraphQL response = data wrapper + requested fields [OK]

Hint: GraphQL results always wrap data inside a 'data' object [OK]

Common Mistakes:

• Omitting the 'data' wrapper in response
• Using wrong field names in response
• Returning arrays instead of objects

4. You wrote this query in GraphQL Playground:

query { user(id: 5) { name email } }

But you get an error. What is the likely cause?

medium

A. GraphQL Playground does not support arguments

B. The query keyword is missing

C. Field names must be uppercase

D. The id argument should be a string, so it needs quotes

Solution

1. Step 1: Check argument types in GraphQL

   GraphQL requires string arguments to be in quotes. Here, id is likely a string but given without quotes.

2. Step 2: Verify other options

   The query keyword is present, field names are case-sensitive but lowercase is valid, and Playground supports arguments. So only The id argument should be a string, so it needs quotes explains the error.

3. Final Answer:

   The id argument should be a string, so it needs quotes -> Option D

4. Quick Check:

   String args need quotes in GraphQL [OK]

Hint: Put quotes around string arguments in queries [OK]

Common Mistakes:

• Leaving string arguments unquoted
• Assuming Playground lacks argument support
• Changing field name case incorrectly

5. You want to explore a new GraphQL API using Playground. Which feature helps you see all available types and fields without writing a query?

hard

A. The Schema Explorer sidebar showing types and fields

B. The Query History panel listing past queries

C. The Response Formatter that beautifies output

D. The Variable Editor for setting query variables

Solution

1. Step 1: Identify features for schema exploration

   GraphQL Playground includes a Schema Explorer sidebar that lists all types, queries, mutations, and fields available in the API.

2. Step 2: Compare other options

   Query History shows past queries, Response Formatter beautifies output, Variable Editor manages variables. Only Schema Explorer shows API schema details.

3. Final Answer:

   The Schema Explorer sidebar showing types and fields -> Option A

4. Quick Check:

   Schema Explorer = view API types and fields [OK]

Hint: Use Schema Explorer to browse API structure easily [OK]

Common Mistakes:

• Confusing Query History with schema browsing
• Thinking Response Formatter shows schema
• Assuming Variable Editor lists fields