gatsby-node.js

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

exports.createPages = async ({ graphql, actions }) => {
  const { createPage } = actions;

  const blogPost = path.resolve(`./src/templates/blog-post.js`);
  const tagTemplate = path.resolve(`src/templates/tags.js`);
  const result = await graphql(
    `
      {
        postsGroup: allMdx(
          filter: { fileAbsolutePath: { regex: "/content/blog/" } }
          sort: { fields: [frontmatter___date], order: DESC }
          limit: 1000
        ) {
          edges {
            node {
              fields {
                slug
              }
              frontmatter {
                title
              }
            }
          }
        }
        tagsGroup: allMdx(
          filter: { fileAbsolutePath: { regex: "/content/blog/" } }
          limit: 2000
        ) {
          group(field: frontmatter___tags) {
            fieldValue
          }
        }
      }
    `,
  );

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

  const posts = result.data.postsGroup.edges;
  const tags = result.data.tagsGroup.group;

  // Create post pages
  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: `/blog${post.node.fields.slug}`,
      component: blogPost,
      context: {
        slug: post.node.fields.slug,
        previous,
        next,
      },
    });
  });

  // Create tag pages
  tags.forEach(tag => {
    createPage({
      path: `/tags/${tag.fieldValue}/`,
      component: tagTemplate,
      context: {
        tag: tag.fieldValue,
      },
    });
  });

  return null;
};

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

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

exports.onCreateWebpackConfig = ({ actions }) => {
  actions.setWebpackConfig({
    resolve: {
      modules: [path.resolve(__dirname, 'src'), 'node_modules'],
    },
  });
};