Express integration in GraphQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Express library.

GraphQL

const express = require('[1]');

Drag options to blanks, or click blank then click option'

Agraphql

Bmongoose

Capollo-server

Dexpress

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'graphql' instead of 'express' will cause an error.

Using 'apollo-server' is for GraphQL server, not Express.

The Express library is imported using require('express'). This allows us to create an Express app.

2fill in blank

medium

Complete the code to create an Express application instance.

GraphQL

const app = [1]();

Drag options to blanks, or click blank then click option'

Aapollo

Bexpress

Cgraphql

Drouter

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'graphql()' will cause an error because it's not a function here.

Using 'router()' is for routing, not app creation.

Calling express() creates a new Express application instance.

3fill in blank

hard

Fix the error in the code to start the Express server on port 4000.

GraphQL

app.listen([1], () => {
  console.log('Server running on port 4000');
});

Drag options to blanks, or click blank then click option'

A4000

B'port 4000'

C'4000'

Dport

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string like '4000' can cause unexpected behavior.

Using 'port' without a value is invalid.

The listen method expects a number for the port, not a string.

4fill in blank

hard

Fill both blanks to add a GraphQL endpoint using Express and Apollo Server.

GraphQL

const [1] = require('express-graphql');
app.use('/graphql', [2]({ schema, graphiql: true }));

Drag options to blanks, or click blank then click option'

AgraphqlHTTP

BexpressGraphQL

CApolloServer

Dgraphql

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'ApolloServer' directly in app.use is incorrect.

Mixing up import names causes errors.

The express-graphql package exports graphqlHTTP which is used as middleware in Express.

5fill in blank

hard

Fill all three blanks to define a simple GraphQL schema and integrate it with Express.

GraphQL

const { [1], GraphQLSchema, GraphQLString } = require('graphql');

const schema = new [2]({
  query: new [3]({
    name: 'RootQueryType',
    fields: {
      hello: {
        type: GraphQLString,
        resolve() {
          return 'Hello world!';
        }
      }
    }
  })
});

Drag options to blanks, or click blank then click option'

AGraphQLObjectType

BGraphQLSchema

CGraphQLString

DGraphQLInt

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing GraphQLSchema and GraphQLObjectType.

Using GraphQLInt instead of GraphQLString for the hello field.

We import GraphQLObjectType and GraphQLSchema from 'graphql'. The schema is created with new GraphQLSchema and the query is a GraphQLObjectType.

Practice

1. What is the main purpose of using express-graphql middleware in an Express app?

easy

A. To create a new database connection

B. To connect a GraphQL schema to the Express server for handling HTTP requests

C. To serve static files like images and CSS

D. To replace Express with a GraphQL server

Solution

1. Step 1: Understand the role of middleware in Express

   Middleware functions in Express handle requests and responses, adding features to the server.

2. Step 2: Identify what express-graphql does

   This middleware connects a GraphQL schema and resolvers to Express, enabling GraphQL queries over HTTP.

3. Final Answer:

   To connect a GraphQL schema to the Express server for handling HTTP requests -> Option B

4. Quick Check:

   express-graphql middleware = Connect GraphQL to Express [OK]

Hint: Middleware connects GraphQL schema to Express HTTP server [OK]

Common Mistakes:

• Thinking it creates a database connection
• Confusing it with static file serving
• Assuming it replaces Express entirely

2. Which of the following is the correct way to use express-graphql middleware in an Express app?

easy

A. app.get('/graphql', graphqlHTTP(mySchema));

B. app.use('/graphql', graphqlHTTP(schema, rootResolver));

C. app.post('/graphql', graphqlHTTP({ rootValue: rootResolver }));

D. app.use('/graphql', graphqlHTTP({ schema: mySchema, rootValue: rootResolver, graphiql: true }));

Solution

1. Step 1: Recall the correct syntax for express-graphql middleware

   The middleware is used with app.use and takes an options object with keys like schema, rootValue, and graphiql.

2. Step 2: Check each option for correct usage

   app.use('/graphql', graphqlHTTP({ schema: mySchema, rootValue: rootResolver, graphiql: true })); correctly uses app.use with an options object including schema, rootValue, and graphiql. Others either misuse method or pass wrong arguments.

3. Final Answer:

   app.use('/graphql', graphqlHTTP({ schema: mySchema, rootValue: rootResolver, graphiql: true })); -> Option D

4. Quick Check:

   express-graphql needs options object with schema and rootValue [OK]

Hint: Use app.use with options object for express-graphql [OK]

Common Mistakes:

• Using app.get or app.post instead of app.use
• Passing schema and rootValue as separate arguments
• Omitting the graphiql option during development

3. Given this Express setup with GraphQL:

const express = require('express');
const { graphqlHTTP } = require('express-graphql');
const { buildSchema } = require('graphql');

const schema = buildSchema(`
  type Query {
    hello: String
  }
`);

const root = {
  hello: () => 'Hello world!'
};

const app = express();
app.use('/graphql', graphqlHTTP({ schema: schema, rootValue: root, graphiql: false }));

app.listen(4000);

What will be the JSON response to this POST query to /graphql?

{"query": "{ hello }"}

medium

A. {"data":{"hello":"Hello world!"}}

B. {"error":"Query not found"}

C. {"data":{"hello":null}}

D. SyntaxError

Solution

1. Step 1: Understand the schema and resolver

   The schema defines a Query type with a field hello returning a String. The root resolver returns 'Hello world!' for hello.

2. Step 2: Analyze the query and response

   The query requests { hello }. The resolver returns 'Hello world!', so the response JSON includes this under data.

3. Final Answer:

   {"data":{"hello":"Hello world!"}} -> Option A

4. Quick Check:

   Query hello returns 'Hello world!' [OK]

Hint: Query matches resolver return value exactly [OK]

Common Mistakes:

• Expecting an error when schema and resolver match
• Confusing null with missing data
• Assuming graphiql affects response format

4. You wrote this Express GraphQL setup:

app.use('/graphql', graphqlHTTP({
  schema: mySchema,
  rootValue: rootResolver
}));

But when you send queries, you get an error: Cannot POST /graphql. What is the likely cause?

medium

A. You did not enable the body parser middleware for JSON

B. You did not define the schema correctly

C. You used app.get instead of app.use

D. You forgot to import express-graphql

Solution

1. Step 1: Understand the error message

   The error 'Cannot POST /graphql' means Express does not recognize POST requests to that route.

2. Step 2: Check middleware setup for POST data

   GraphQL POST requests send JSON body. Express needs body parser middleware (like express.json()) to parse JSON bodies before graphqlHTTP.

3. Final Answer:

   You did not enable the body parser middleware for JSON -> Option A

4. Quick Check:

   Missing JSON body parser causes POST errors [OK]

Hint: Always add express.json() before graphqlHTTP for POST [OK]

Common Mistakes:

• Assuming graphqlHTTP handles JSON parsing automatically
• Confusing app.use with app.get
• Blaming schema definition for routing errors

5. You want to add a new Query field user(id: ID!): User to your GraphQL schema in Express. The User type has fields id and name. Which of the following shows the correct way to extend the schema and resolver for this, assuming you have a getUserById function?

hard

A. Schema: type Query { user(id: String): User } and resolver: { user: (id) => getUserById(id) }

B. Schema: type Query { user: User } and resolver: { user: () => getUserById() }

C. Schema: type Query { user(id: ID!): User } and resolver: { user: ({id}) => getUserById(id) }

D. Schema: type Query { user(id: ID!): User } and resolver: { user: (args) => getUserById(args) }

Solution

1. Step 1: Define schema with required argument and User type

   The schema must declare user(id: ID!): User to require an ID argument and return a User object.

2. Step 2: Write resolver matching argument destructuring

   The resolver function receives an object with arguments, so destructure {id} and pass it to getUserById.

3. Final Answer:

   Schema: type Query { user(id: ID!): User } and resolver: { user: ({id}) => getUserById(id) } -> Option C

4. Quick Check:

   Schema arg ID! and resolver destructure args [OK]

Hint: Destructure args object in resolver for required ID [OK]

Common Mistakes:

• Not marking ID as non-null with !
• Passing args incorrectly in resolver
• Using wrong argument type in schema