gatsby-node.js

'use strict';

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

module.exports = {
  createPages: ({graphql, boundActionCreators: {createPage}}) => {
    return new Promise((resolve, reject) => {
      const blogPost = path.resolve('./src/templates/post.js');

      resolve(
        graphql(
          `
            {
              allMarkdownRemark(sort: { fields: [frontmatter___date], order: DESC }, limit: 1000) {
                edges {
                  node {
                    fields {
                      slug
                    }
                    frontmatter {
                      title
                    }
                  }
                }
              }
            }
          `
        ).then((result) => {
          if (result.errors) {
            console.log(result.errors);
            reject(result.errors);
          }

          const posts = result.data.allMarkdownRemark.edges;

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

            createPage({
              path: post.node.fields.slug,
              component: blogPost,
              context: {
                slug: post.node.fields.slug,
                previous,
                next
              }
            });
          });
        })
      );
    });
  },
  onCreateNode: ({node, boundActionCreators, getNode}) => {
    const {createNodeField} = boundActionCreators;

    if (node.internal.type === `MarkdownRemark`) {
      const value = createFilePath({node, getNode});

      createNodeField({
        name: `slug`,
        node,
        value
      });
    }
  }
};