Apollo Client setup in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Apollo Client used for in a GraphQL application?

Apollo Client is a tool that helps your app talk to a GraphQL server. It fetches data, manages it locally, and updates your app when data changes.

beginner

Which package do you install to use Apollo Client in a JavaScript project?

You install the @apollo/client package to use Apollo Client in your JavaScript or React project.

beginner

What is the purpose of ApolloProvider in Apollo Client setup?

ApolloProvider wraps your app and makes the Apollo Client available to all components so they can run GraphQL queries and mutations.

intermediate

What is the role of InMemoryCache in Apollo Client?

InMemoryCache stores the data fetched from the GraphQL server locally in memory. It helps Apollo Client manage and reuse data efficiently.

beginner

How do you specify the GraphQL server URL in Apollo Client setup?

You provide the server URL in the uri option when creating an ApolloClient instance, like new ApolloClient({ uri: 'https://your-server.com/graphql' }).

Which of these is the correct package to install for Apollo Client?

A apollo-graphql

B apollo-server

C graphql-client

D @apollo/client

The correct package for Apollo Client in frontend apps is @apollo/client. Others are for server or unrelated.

What does InMemoryCache do in Apollo Client?

A Stores data locally in memory for quick access

B Sends queries to the server

C Manages user authentication

D Creates GraphQL schemas

InMemoryCache keeps fetched data in memory so Apollo Client can reuse it without asking the server again.

What component wraps your React app to provide Apollo Client functionality?

A ApolloWrapper

B GraphQLProvider

C ApolloProvider

D ClientWrapper

ApolloProvider is the official component that makes Apollo Client available to your React components.

Where do you specify the GraphQL server URL in Apollo Client?

A In the <code>uri</code> option when creating ApolloClient

B Inside <code>ApolloProvider</code> props

C In the <code>InMemoryCache</code> settings

D In the GraphQL query itself

The server URL is set in the uri option when you create the ApolloClient instance.

Which of these is NOT part of the basic Apollo Client setup?

A Creating an ApolloClient instance

B Writing GraphQL server resolvers

C Installing @apollo/client package

D Wrapping the app with ApolloProvider

Writing server resolvers is done on the backend, not part of the Apollo Client setup on the frontend.

Describe the steps to set up Apollo Client in a React app from installation to making it available in components.

Think about what you need to install, create, and wrap.

Explain the role of InMemoryCache in Apollo Client and why it is important.

Consider how caching helps your app work faster.

Practice

1. What is the main purpose of Apollo Client in a GraphQL application?

easy

A. To connect your app to a GraphQL server and manage data

B. To create a new GraphQL server

C. To style your app's user interface

D. To store data permanently on the server

Solution

1. Step 1: Understand Apollo Client's role

   Apollo Client is designed to connect your app to a GraphQL server and handle data fetching and caching.

2. Step 2: Differentiate from other roles

   Creating servers or styling UI are not responsibilities of Apollo Client.

3. Final Answer:

   To connect your app to a GraphQL server and manage data -> Option A

4. Quick Check:

   Apollo Client = Connect and manage data [OK]

Hint: Apollo Client connects app to server and manages data [OK]

Common Mistakes:

• Confusing Apollo Client with server creation tools
• Thinking Apollo Client styles the UI
• Assuming Apollo Client stores data permanently on server

2. Which of the following is the correct way to create an Apollo Client instance with a server URL 'https://api.example.com/graphql'?

easy

A. const client = new ApolloClient({ endpoint: 'https://api.example.com/graphql' });

B. const client = ApolloClient({ url: 'https://api.example.com/graphql', cache: new Cache() });

C. const client = new ApolloClient({ uri: 'https://api.example.com/graphql', cache: new InMemoryCache() });

D. const client = new ApolloClient('https://api.example.com/graphql');

Solution

1. Step 1: Check Apollo Client constructor syntax

   The correct syntax uses 'new ApolloClient' with an object containing 'uri' and 'cache' properties.

2. Step 2: Verify property names and cache setup

   The property for the server URL is 'uri', and the cache should be an instance of 'InMemoryCache'.

3. Final Answer:

   const client = new ApolloClient({ uri: 'https://api.example.com/graphql', cache: new InMemoryCache() }); -> Option C

4. Quick Check:

   Use 'uri' and 'InMemoryCache' in ApolloClient setup [OK]

Hint: Use 'uri' and 'new InMemoryCache()' when creating Apollo Client [OK]

Common Mistakes:

• Using 'url' or 'endpoint' instead of 'uri'
• Not using 'new' keyword with ApolloClient
• Omitting the cache property or using wrong cache class

3. Given this Apollo Client setup code, what will console.log(client.cache.extract()) output immediately after creation?

const client = new ApolloClient({
  uri: 'https://api.example.com/graphql',
  cache: new InMemoryCache()
});
console.log(client.cache.extract());

medium

A. A string with the server URL

B. null

C. An error because cache is not initialized

D. {} (an empty object)

Solution

1. Step 1: Understand InMemoryCache initial state

   When a new InMemoryCache is created, it starts empty with no stored data.

2. Step 2: Check what extract() returns

   The extract() method returns the current cache contents as an object. Since no queries ran yet, it returns an empty object {}.

3. Final Answer:

   {} (an empty object) -> Option D

4. Quick Check:

   New cache extract() = empty object {} [OK]

Hint: New cache is empty; extract() returns {} [OK]

Common Mistakes:

• Expecting data before any query runs
• Thinking extract() returns null or error
• Confusing cache contents with server URL

4. Identify the error in this Apollo Client setup code:

const client = new ApolloClient({
  url: 'https://api.example.com/graphql',
  cache: new InMemoryCache()
});

medium

A. Missing 'new' keyword before InMemoryCache

B. Property 'url' should be 'uri'

C. ApolloClient should not be called with 'new'

D. Cache property should be a string, not an object

Solution

1. Step 1: Check property names in Apollo Client config

   The correct property for the server address is 'uri', not 'url'.

2. Step 2: Verify cache instantiation

   The cache is properly instantiated as new InMemoryCache(). The primary error is the incorrect property name.

3. Final Answer:

   Property 'url' should be 'uri' -> Option B

4. Quick Check:

   Use 'uri' property for server URL [OK]

Hint: Use 'uri' not 'url' for server address in Apollo Client [OK]

Common Mistakes:

• Using 'url' instead of 'uri'
• Forgetting 'new' before InMemoryCache()
• Thinking ApolloClient is called without 'new'

5. You want to set up Apollo Client to connect to a GraphQL server and cache data efficiently. Which of the following code snippets correctly sets up the client and explains why this setup is best for performance?

hard

A. const client = new ApolloClient({ uri: 'https://api.example.com/graphql', cache: new InMemoryCache() }); // Efficient caching and server connection

B. const client = new ApolloClient({ uri: 'https://api.example.com/graphql' }); // No cache used, faster queries

C. const client = new ApolloClient({ cache: new InMemoryCache() }); // No server URI, so no connection

D. const client = ApolloClient({ uri: 'https://api.example.com/graphql', cache: new InMemoryCache() }); // Missing 'new' keyword

Solution

1. Step 1: Confirm correct Apollo Client instantiation

   const client = new ApolloClient({ uri: 'https://api.example.com/graphql', cache: new InMemoryCache() }); // Efficient caching and server connection uses 'new ApolloClient' with both 'uri' and 'cache' properly set, which is required for connection and caching.

2. Step 2: Understand why caching improves performance

   Using 'InMemoryCache' stores query results locally, reducing network requests and speeding up data access.

3. Final Answer:

   const client = new ApolloClient({ uri: 'https://api.example.com/graphql', cache: new InMemoryCache() }); // Efficient caching and server connection -> Option A

4. Quick Check:

   Use 'new ApolloClient' with 'uri' and 'InMemoryCache' for best performance [OK]

Hint: Always use 'new ApolloClient' with 'uri' and 'InMemoryCache' [OK]

Common Mistakes:

• Omitting cache reduces performance
• Missing 'new' causes errors
• Not specifying server URI prevents connection