gatsby-node.js

/**
 * Implement Gatsby's Node APIs in this file.
 *
 * See: https://www.gatsbyjs.org/docs/node-apis/
 */

const path = require(`path`);
const { createFilePath } = require(`gatsby-source-filesystem`);

exports.createPages = async ({ graphql, actions }) => {
  const { createPage } = actions;
  const blogPost = path.resolve(`./src/templates/blogPost.js`);

  const result = await graphql(`
    {
      allMdx(sort: { order: DESC, fields: frontmatter___date }) {
        nodes {
          fields {
            slug
          }
        }
      }
    }
  `);

  if (result.errors) {
    throw result.errors;
  }

  // Create blog posts pages.
  const posts = result.data.allMdx.nodes;

  posts.forEach((post, index) => {
    const previous = index === posts.length - 1 ? null : posts[index + 1];
    const next = index === 0 ? null : posts[index - 1];

    createPage({
      path: post.fields.slug,
      component: blogPost,
      context: {
        slug: post.fields.slug,
        previous,
        next,
      },
    });
  });
};

exports.onCreateNode = ({ node, actions, getNode }) => {
  const { createNodeField } = actions;

  if (node.internal.type === `Mdx`) {
    const value = createFilePath({ node, getNode });
    createNodeField({
      name: `slug`,
      node,
      value,
    });
  }
};