Gatsby is a powerful static site generator based on React that enables developers to build fast and scalable websites and applications. One of the key aspects of building effective websites is efficiently displaying data to users. In Gatsby, data display can be achieved using a combination of GraphQL, React components, and third-party data sources like headless CMSs, APIs, and local files.

In this article, we will explore the process of fetching and displaying data in a Gatsby application, focusing on the key principles, strategies, and best practices for rendering data effectively.

1. Understanding Gatsby's Data Layer

Gatsby's data layer is built around GraphQL, which acts as a query language that allows developers to request exactly the data they need. Gatsby integrates deeply with GraphQL, making it easy to pull data from various sources like Markdown files, JSON files, or external APIs and display it within React components.

The steps to display data in Gatsby typically include:

• Fetching data from an external or internal source
• Structuring the data using GraphQL queries
• Displaying the data using React components

2. Setting Up GraphQL Queries in Gatsby

Gatsby comes with a built-in GraphQL layer that allows you to access your data sources easily. You can use GraphQL queries to extract data from:

• Local files such as Markdown or JSON
• CMS platforms like Contentful, Strapi, or WordPress
• APIs and databases

Example 1: Querying Markdown Data

Suppose you are building a blog, and you have written your posts in Markdown files. You can query the Markdown files using Gatsby’s gatsby-transformer-remark plugin and display the content in your React components.

export const query = graphql`
  query BlogPostQuery {
    allMarkdownRemark {
      edges {
        node {
          frontmatter {
            title
            date
          }
          excerpt
        }
      }
    }
  }
`

You can then render the fetched blog posts in your component using JSX:

const Blog = ({ data }) => (
  <div>
    {data.allMarkdownRemark.edges.map(({ node }) => (
      <div key={node.id}>
        <h2>{node.frontmatter.title}</h2>
        <p>{node.excerpt}</p>
        <small>{node.frontmatter.date}</small>
      </div>
    ))}
  </div>
)

Example 2: Querying Data from CMS (Contentful)

If you're using a headless CMS like Contentful, you can query your data by installing the gatsby-source-contentful plugin, which integrates Gatsby with Contentful’s API. Here's an example of fetching blog posts from Contentful:

export const query = graphql`
  query ContentfulBlogPostQuery {
    allContentfulBlogPost {
      edges {
        node {
          title
          publishedDate(formatString: "MMMM Do, YYYY")
          body {
            childMarkdownRemark {
              excerpt
            }
          }
        }
      }
    }
  }
`

You can now render the data similarly to how you would with Markdown:

const Blog = ({ data }) => (
  <div>
    {data.allContentfulBlogPost.edges.map(({ node }) => (
      <div key={node.id}>
        <h2>{node.title}</h2>
        <p>{node.body.childMarkdownRemark.excerpt}</p>
        <small>{node.publishedDate}</small>
      </div>
    ))}
  </div>
)

3. Rendering External Data via APIs

While Gatsby’s static data sources (e.g., Markdown, CMS) are great, there may be cases where you need to fetch external data dynamically from APIs. You can use the useEffect hook in React to fetch data and display it on the client side. For example, here’s how you can fetch data from an external API like a REST endpoint or GraphQL service:

import React, { useEffect, useState } from "react";

const DataDisplay = () => {
  const [data, setData] = useState([]);

  useEffect(() => {
    // Fetch data from an external API
    fetch('https://api.example.com/data')
      .then(response => response.json())
      .then(result => setData(result))
      .catch(error => console.error('Error fetching data:', error));
  }, []);

  return (
    <div>
      {data.map(item => (
        <div key={item.id}>
          <h2>{item.name}</h2>
          <p>{item.description}</p>
        </div>
      ))}
    </div>
  );
};

export default DataDisplay;

4. Optimizing Data Display with Gatsby

Gatsby offers several ways to optimize data display and enhance performance:

Pagination

When displaying large datasets, it’s essential to paginate data to improve page load times and make content more manageable. Gatsby’s createPages API can be used to generate paginated pages dynamically.

const Blog = ({ pageContext, data }) => {
  const { currentPage, numPages } = pageContext;

  return (
    <div>
      {data.allMarkdownRemark.edges.map(({ node }) => (
        <div key={node.id}>
          <h2>{node.frontmatter.title}</h2>
          <p>{node.excerpt}</p>
        </div>
      ))}

      <Pagination currentPage={currentPage} numPages={numPages} />
    </div>
  );
};

Lazy Loading

Lazy loading is a technique that defers loading non-essential resources, improving performance. For example, Gatsby’s gatsby-image can optimize images, and React.lazy or dynamic imports can defer the loading of components.

import { LazyLoadImage } from 'react-lazy-load-image-component';

<LazyLoadImage
  alt="example"
  height={300}
  effect="blur"
  src="path/to/image.jpg" />

Static Site Generation

Gatsby’s build process pre-renders pages into static HTML, significantly improving performance. However, it also allows you to fetch and inject dynamic content at runtime using client-side rendering.

5. Data Visualization with Gatsby

Displaying data effectively sometimes involves visualizations like charts and graphs. You can integrate data visualization libraries, such as Chart.js or D3.js, into your Gatsby project to render visual data representations.

import { Line } from "react-chartjs-2";

const data = {
  labels: ['January', 'February', 'March', 'April', 'May'],
  datasets: [
    {
      label: 'Sales',
      data: [65, 59, 80, 81, 56],
      fill: false,
      backgroundColor: 'rgb(75, 192, 192)',
      borderColor: 'rgba(75, 192, 192, 0.2)',
    },
  ],
};

const MyChart = () => (
  <div>
    <h2>Sales Over Time</h2>
    <Line data={data} />
  </div>
);

Conclusion

Displaying data in Gatsby is a flexible and efficient process, thanks to its integration with GraphQL and its React-based architecture. Whether you are fetching data from local files, CMSs, or APIs, Gatsby provides a solid foundation for building high-performance web applications with rich data display capabilities. By implementing pagination, lazy loading, and other optimization techniques, you can ensure that your Gatsby site remains fast and responsive, even when handling large datasets.