REST vs GraphQL awareness in Express - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding REST API request methods

Which HTTP method is typically used in REST APIs to update an entire resource?

A PUT

B POST

C GET

D DELETE

💡 Hint

Think about which method replaces the whole resource.

In REST, PUT is used to update or replace an entire resource. POST is usually for creating, GET for reading, and DELETE for removing.

❓ component_behavior

intermediate

GraphQL query response shape

Given a GraphQL query requesting only the name and age fields of a user, what will the response JSON look like?

Express

query { user(id: "1") { name age } }

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

B {"user": {"name": "Alice", "age": 30}}

C {"data": {"user": {"id": "1", "name": "Alice", "age": 30}}}

D {"data": {"user": {"name": "Alice", "age": 30}}}

💡 Hint

GraphQL responses always wrap data inside a 'data' key.

GraphQL responses wrap the requested data inside a data object. Only the requested fields appear. Here, name and age are included, but not id.

📝 Syntax

advanced

Express route for REST vs GraphQL

Which Express route setup correctly handles a GraphQL POST request at '/graphql'?

Express

const express = require('express');
const app = express();
// Which option is correct?

A app.post('/graphql', (req, res) => { res.send('GraphQL endpoint'); });

B app.get('/graphql', (req, res) => { res.send('GraphQL endpoint'); });

C app.delete('/graphql', (req, res) => { res.send('GraphQL endpoint'); });

D app.put('/graphql', (req, res) => { res.send('GraphQL endpoint'); });

💡 Hint

GraphQL queries and mutations are usually sent via POST requests.

GraphQL servers typically accept POST requests at a single endpoint, often '/graphql'. Using app.post matches this pattern.

❓ state_output

advanced

REST API response status codes

What HTTP status code should a REST API return after successfully deleting a resource?

A 200 OK

B 201 Created

C 204 No Content

D 404 Not Found

💡 Hint

The response usually has no body after deletion.

After a successful deletion, REST APIs commonly return 204 No Content to indicate success without a response body.

🔧 Debug

expert

Debugging GraphQL query error in Express

An Express server with GraphQL returns an error: Cannot read property 'data' of undefined. Which code snippet is the likely cause?

Express

app.post('/graphql', async (req, res) => {
  const result = await graphql(schema, req.body.query);
  res.json(result.data);
});

A The 'graphql' function returns a promise resolving to an object with 'data' property, so this code is correct.

B The 'graphql' function returns a promise resolving to an object with 'data' and 'errors', but the code should check if 'result' is defined before accessing 'result.data'.

C The 'graphql' function returns a promise resolving to an object with 'data' and 'errors', but if 'result' is undefined, accessing 'result.data' causes the error.

D The 'graphql' function returns an object with 'data' nested inside 'result', so accessing 'result.data' is correct.

💡 Hint

Check if the promise resolves correctly and if the result is defined before accessing properties.

The error occurs because result might be undefined if the promise rejects or the call fails. The code should handle errors and check if result exists before accessing result.data.

Practice

1. Which statement best describes the main difference between REST and GraphQL in an Express API?

easy

A. REST uses multiple URLs and HTTP methods; GraphQL uses a single URL with flexible queries.

B. REST uses a single URL and flexible queries; GraphQL uses multiple URLs and HTTP methods.

C. REST and GraphQL both use multiple URLs but differ in data format.

D. REST and GraphQL are identical in how they handle data fetching.

Solution

1. Step 1: Understand REST API structure

   REST APIs use different URLs (endpoints) for different resources and HTTP methods like GET, POST, PUT, DELETE to perform actions.

2. Step 2: Understand GraphQL API structure

   GraphQL uses a single endpoint URL and clients specify exactly what data they want in the query, making it flexible.

3. Final Answer:

   REST uses multiple URLs and HTTP methods; GraphQL uses a single URL with flexible queries. -> Option A

4. Quick Check:

   REST vs GraphQL = multiple URLs vs single URL [OK]

Hint: REST = many URLs; GraphQL = one URL with queries [OK]

Common Mistakes:

• Thinking GraphQL uses multiple URLs like REST
• Confusing HTTP methods usage between REST and GraphQL
• Believing REST and GraphQL are the same

2. Which Express route setup correctly represents a REST API endpoint for getting a user by ID?

easy

A. app.put('/user', (req, res) => { /* fetch user */ });

B. app.post('/user/:id', (req, res) => { /* fetch user */ });

C. app.get('/user/:id', (req, res) => { /* fetch user */ });

D. app.get('/graphql', (req, res) => { /* fetch user */ });

Solution

1. Step 1: Identify correct HTTP method for fetching data

   GET method is used to retrieve data in REST APIs.

2. Step 2: Check URL pattern for resource identification

   /user/:id correctly uses a URL parameter to specify which user to fetch.

3. Final Answer:

   app.get('/user/:id', (req, res) => { /* fetch user */ }); -> Option C

4. Quick Check:

   GET + /user/:id = fetch user [OK]

Hint: GET method + URL with :id fetches resource [OK]

Common Mistakes:

• Using POST instead of GET for fetching data
• Using GraphQL endpoint for REST question
• Using PUT method which is for updates

3. Given this Express GraphQL setup, what will the client receive when querying for { user(id: "1") { name } }?

const { graphqlHTTP } = require('express-graphql');
const schema = buildSchema(`
  type Query {
    user(id: ID!): User
  }
  type User {
    id: ID
    name: String
    email: String
  }
`);
const root = {
  user: ({ id }) => ({ id, name: 'Alice', email: '[e-mail]' })
};
app.use('/graphql', graphqlHTTP({ schema, rootValue: root, graphiql: true }));

medium

A. {"data":{"user":{"id":"1","name":"Alice","email":"[e-mail]"}}}

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

C. {"error":"Field 'user' not found"}

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

Solution

1. Step 1: Understand the GraphQL query

   The query requests only the name field of the user with id "1".

2. Step 2: Check resolver returns full user object

   The resolver returns id, name, and email, but GraphQL returns only requested fields.

3. Final Answer:

   {"data":{"user":{"name":"Alice"}}} -> Option B

4. Quick Check:

   GraphQL returns only requested fields [OK]

Hint: GraphQL returns only requested fields, not full object [OK]

Common Mistakes:

• Expecting all fields returned regardless of query
• Confusing error responses with valid data
• Assuming REST style full object return

4. Identify the error in this Express REST route that causes it to always return an empty response:

app.get('/users/:id', (req, res) => {
  const user = users.find(u => u.id === req.params.id);
  if (user) {
    res.json(user);
  }
  res.end();
});

medium

A. The route path should be '/user/:id' not '/users/:id'.

B. The route should use POST instead of GET.

C. The user lookup uses incorrect comparison operator.

D. res.end() is called even after sending a response, causing empty output.

Solution

1. Step 1: Analyze response flow

   If user is found, res.json(user) sends response, but code continues to res.end() which sends empty response again.

2. Step 2: Understand Express response behavior

   Calling res.end() after res.json() can cause the response to be overwritten or cause errors.

3. Final Answer:

   res.end() is called even after sending a response, causing empty output. -> Option D

4. Quick Check:

   Only send one response per request [OK]

Hint: Send only one response; avoid res.end() after res.json() [OK]

Common Mistakes:

• Using wrong HTTP method for fetching
• Assuming path name causes empty response
• Ignoring that res.end() can overwrite response

5. You want to build an Express API that allows clients to fetch user data with flexible fields and avoid multiple endpoints. Which approach is best and why?

hard

A. Use GraphQL with a single endpoint letting clients specify exactly which fields they want.

B. Use REST but return all fields for every resource to avoid multiple endpoints.

C. Use REST with multiple endpoints for each resource and HTTP methods for actions.

D. Use GraphQL but create multiple endpoints for each query type.

Solution

1. Step 1: Identify requirement for flexible fields and fewer endpoints

   Clients want to specify fields and avoid many URLs.

2. Step 2: Match approach to requirement

   GraphQL uses one endpoint and allows clients to request exactly needed fields, fitting the requirement.

3. Final Answer:

   Use GraphQL with a single endpoint letting clients specify exactly which fields they want. -> Option A

4. Quick Check:

   Flexible fields + single endpoint = GraphQL [OK]

Hint: Flexible data + one URL = GraphQL [OK]

Common Mistakes:

• Choosing REST and returning all fields wastes bandwidth
• Using GraphQL with multiple endpoints defeats its purpose
• Confusing REST flexibility with GraphQL's query power