透過 REST API 上的 GraphQL 增強 React 應用程式

In the rapidly changing world of web development, optimizing and scaling applications is always an issue. React.js had an extraordinary success for frontend development as a tool, that provides a robust way to create user interfaces. But it gets complicated with growing applications, especially when it comes to multiple REST API endpoints. Concerns such as over-fetching, where excessive data than required can be a source of performance bottleneck and a poor user experience.

Among the solutions to these challenges is adopting the use of GraphQL with React applications. If your backend has multiple REST endpoints, then introducing a GraphQL layer that internally calls your REST API endpoints can enhance your application from overfetching and streamline your frontend application. In this article, you will find how to use it, the advantages and disadvantages of this approach, various challenges; and how to address them. We will also dive deeper into some practical examples of how GraphQL can help you improve the ways you work with your data.

Overfetching in REST APIs

In REST APIs, Over-fetching occurs when the amount of data that the API delivers to the client is more than what the client requires. This is a common problem with REST APIs, which often returns a fixed Object or Response Schema. To better understand this problem let us consider an example.

Consider a user profile page where the it is only required to show the user’s name and email. With a typical REST API, fetching the user data might look like this:

fetch('/api/users/1')
  .then(response => response.json())
  .then(user => {
    // Use the user's name and profilePicture in the UI
  });

The API response will include unnecessary data:

{
  "id": 1,
  "name": "John Doe",
  "profilePicture": "/images/john.jpg",
  "email": "john@example.com",
  "address": "123 Denver St",
  "phone": "111-555-1234",
  "preferences": {
    "newsletter": true,
    "notifications": true
  },
  // ...more details
}

Although the application only requires the name and email fields of the user, the API returns the whole user object. This additional data often increases the payload size, take more bandwidth and can eventually slow down the application when used on a device with limited resources or a slow network connection.

GraphQL as a Solution

GraphQL addresses the overfetching problem by allowing clients to request exactly the data they need. By integrating a GraphQL server into your application, you can create a flexible and efficient data-fetching layer that communicates with your existing REST APIs.

How It Works

1. GraphQL Server Setup: You introduce a GraphQL server that serves as an intermediary between your React frontend and the REST APIs.
2. Schema Definition: You define a GraphQL schema that specifies the data types and queries your frontend requires.
3. Resolvers Implementation: You implement resolvers in the GraphQL server that fetch data from the REST APIs and return only the necessary fields.
4. Frontend Integration: You update your React application to use GraphQL queries instead of direct REST API calls.

This approach allows you to optimize data fetching without overhauling your existing backend infrastructure.

Implementing GraphQL in a React Application

Let’s look at how to set up a GraphQL server and integrate it into a React application.

Install Dependencies:

npm install apollo-server graphql axios

Define the Schema

Create a file called schema.js:

const { gql } = require('apollo-server');

const typeDefs = gql`
  type User {
    id: ID!
    name: String
    email: String  // Ensure this matches exactly with the frontend query
  }

  type Query {
    user(id: ID!): User
  }
`;

module.exports = typeDefs;

This schema defines a User type and a user query that fetches a user by ID.

Implement Resolvers

Create a file called resolvers.js:

const resolvers = {
  Query: {
    user: async (_, { id }) => {
      try {
        const response = await fetch(`https://jsonplaceholder.typicode.com/users/${id}`);
        const user = await response.json();

        return {
          id: user.id,
          name: user.name,
          email: user.email,  // Return email instead of profilePicture
        };
      } catch (error) {
        throw new Error(`Failed to fetch user: ${error.message}`);
      }
    },
  },
};

module.exports = resolvers;

The resolver for the user query fetches data from the REST API and returns only the required fields.

We will use https://jsonplaceholder.typicode.com/for our fake REST API.

Set Up the Server

Create a server.js file:

const { ApolloServer } = require('apollo-server');
const typeDefs = require('./schema');
const resolvers = require('./resolvers');

const server = new ApolloServer({
  typeDefs,
  resolvers,
});

server.listen({ port: 4000 }).then(({ url }) => {
  console.log(`GraphQL Server ready at ${url}`);
});

Start the server:

node server.js

Your GraphQL server is live at http://localhost:4000/graphql and if you query your server, it will take you to this page.

Integrating with the React Application

We will now change the React application to use the GraphQL API.

Install Apollo Client

npm install @apollo/client graphql

Configure Apollo Client

import { ApolloClient, InMemoryCache } from '@apollo/client';

const client = new ApolloClient({
  uri: 'http://localhost:4000', 
  cache: new InMemoryCache(),
});

Write the GraphQL Query

const GET_USER = gql`
  query GetUser($id: ID!) {
    user(id: $id) {
      id
      name
      email
    }
  }
`;

Now integrate the above pieces of codes with your react app. Here is a simple react app below which lets a user select the userId and displays the information:

import { useState } from 'react';
import { ApolloClient, InMemoryCache, ApolloProvider, gql, useQuery } from '@apollo/client';
import './App.css';  // Link to the updated CSS

const client = new ApolloClient({
  uri: 'http://localhost:4000',  // Ensure this is the correct URL for your GraphQL server
  cache: new InMemoryCache(),
});

const GET_USER = gql`
  query GetUser($id: ID!) {
    user(id: $id) {
      id
      name
      email
    }
  }
`;

const User = ({ userId }) => {
  const { loading, error, data } = useQuery(GET_USER, {
    variables: { id: userId },
  });

  if (loading) return <p>Loading...</p>;
  if (error) return <p>Error: {error.message}</p>;

  return (
    <div className="user-container">
      <h2>{data.user.name}</h2>
      <p>Email: {data.user.email}</p>
    </div>
  );
};

const App = () => {
  const [selectedUserId, setSelectedUserId] = useState("1");

  return (
    <ApolloProvider client={client}>
      <div className="app-container">
        <h1 className="title">GraphQL User Lookup</h1>
        <div className="dropdown-container">
          <label htmlFor="userSelect">Select User ID:</label>
          <select
            id="userSelect"
            value={selectedUserId}
            onChange={(e) => setSelectedUserId(e.target.value)}
          >
            {Array.from({ length: 10 }, (_, index) => (
              <option key={index + 1} value={index + 1}>
                {index + 1}
              </option>
            ))}
          </select>
        </div>
        <User userId={selectedUserId} />
      </div>
    </ApolloProvider>
  );
};

export default App;

Result:

Simple User

Working with Multiple Endpoints

Imagine a scenario where you need to retrieve a specific user’s posts, along with the individual comments on each post. Instead of making three separate API calls from your frontend React app and dealing with unnecessary data, you can streamline the process with GraphQL. By defining a schema and crafting a GraphQL query, you can request only the exact data your UI requires, all in one efficient request.

We need to fetch user data, their posts, and comments for each post from the different endpoints. We’ll use fetch to gather data from the multiple endpoints and return it via GraphQL.

Update Resolvers

const fetch = require('node-fetch');

const resolvers = {
  Query: {
    user: async (_, { id }) => {
      try {
        // fetch user
        const userResponse = await fetch(`https://jsonplaceholder.typicode.com/users/${id}`);
        const user = await userResponse.json();

        // fetch posts for a user
        const postsResponse = await fetch(`https://jsonplaceholder.typicode.com/posts?userId=${id}`);
        const posts = await postsResponse.json();

        // fetch comments for a post
        const postsWithComments = await Promise.all(
          posts.map(async (post) => {
            const commentsResponse = await fetch(`https://jsonplaceholder.typicode.com/comments?postId=${post.id}`);
            const comments = await commentsResponse.json();
            return { ...post, comments };
          })
        );

        return {
          id: user.id,
          name: user.name,
          email: user.email,
          posts: postsWithComments,
        };
      } catch (error) {
        throw new Error(`Failed to fetch user data: ${error.message}`);
      }
    },
  },
};

module.exports = resolvers;

Update GraphQL Schema

const { gql } = require('apollo-server');

const typeDefs = gql`
  type Comment {
    id: ID!
    name: String
    email: String
    body: String
  }

  type Post {
    id: ID!
    title: String
    body: String
    comments: [Comment]
  }

  type User {
    id: ID!
    name: String
    email: String
    posts: [Post]
  }

  type Query {
    user(id: ID!): User
  }
`;

module.exports = typeDefs;

Server setup in server.js remains same. Once we update the React.js code, we get the below output:

Detailed User

Benefits of This Approach

Integrating GraphQL into your React application provides several advantages:

Eliminating Overfetching

A key feature of GraphQL is that it only fetches exactly what you request. The server only returns the requested fields and ensures that the amount of data transferred over the network is reduced by serving only what the query demands and thus improving performance.

Simplifying Frontend Code

GraphQL enables you to get the needful information in a single query regardless of their origin. Internally it could be making 3 API calls to get the information. This helps to simplify your frontend code because now you don’t need to orchestrate different async requests and combine their results.

Improving Developer’s Experience

A strong typing and schema introspection offer better tooling and error checking than in the traditional API implementation. Further to that, there are interactive environments where developers can build and test queries, including GraphiQL or Apollo Explorer.

Addressing Complexities and Challenges

This approach has some advantages but it also introduces some challenges that have to be managed.

Additional Backend Layer

The introduction of the GraphQL server creates an extra layer in your backend architecture and if not managed properly, it becomes a single point of failure.

Solution: Pay attention to error handling and monitoring. Containerization and orchestration tools like Docker and Kubernetes can help manage scalability and reliability.

Potential Performance Overhead

The GraphQL server may make multiple REST API calls to resolve a single query, which can introduce latency and overhead to the system.

Solution: Cache the results to avoid making several calls to the API. There exist some tools such as DataLoader which can handle the process of batching and caching of requests.

Conclusion

"Simplicity is the ultimate sophistication" — Leonardo da Vinci

Integrating GraphQL into your React application is more than just a performance optimization — it’s a strategic move towards building more maintainable, scalable, and efficient applications. By addressing overfetching and simplifying data management, you not only enhance the user experience but also empower your development team with better tools and practices.

While the introduction of a GraphQL layer comes with its own set of challenges, the benefits often outweigh the complexities. By carefully planning your implementation, optimizing your resolvers, and securing your endpoints, you can mitigate potential drawbacks. Moreover, the flexibility that GraphQL offers can future-proof your application as it grows and evolves.

Embracing GraphQL doesn’t mean abandoning your existing REST APIs. Instead, it allows you to leverage their strengths while providing a more efficient and flexible data access layer for your frontend applications. This hybrid approach combines the reliability of REST with the agility of GraphQL, giving you the best of both worlds.

If you’re ready to take your React application to the next level, consider integrating GraphQL into your data fetching strategy. The journey might present challenges, but the rewards — a smoother development process, happier developers, and satisfied users — make it a worthwhile endeavor.

Full Code Available

You can find the full code for this implementation on my GitHub repository: GitHub Link.

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