gatsby-node.js

const path = require(`path`)
const { createFilePath } = require(`gatsby-source-filesystem`)
const kebabCase = require("lodash").kebabCase

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

  const blogPost = path.resolve(`./src/templates/blog-post.tsx`)
  const tagTemplate = path.resolve(`./src/templates/tag.tsx`)
  const newsletterTemplate = path.resolve(`./src/templates/newsletter.tsx`)
  const rootPagesTemplate = path.resolve(`./src/templates/root.tsx`)

  const result = await graphql(
    `
      {
        posts: allMarkdownRemark(
          sort: { fields: [frontmatter___date], order: DESC }
          limit: 1000
          filter: { frontmatter: { newsletter: { ne: true } } }
        ) {
          edges {
            node {
              fields {
                slug
              }
              frontmatter {
                title
                tags
                published
              }
            }
          }
        }
        tagsGroup: allMarkdownRemark(limit: 2000) {
          group(field: frontmatter___tags) {
            fieldValue
          }
        }
        issues: allMarkdownRemark(
          sort: { fields: [frontmatter___date], order: DESC }
          limit: 1000
          filter: { frontmatter: { newsletter: { eq: true } } }
        ) {
          edges {
            node {
              fields {
                slug
              }
              frontmatter {
                title
                tags
                published
              }
            }
          }
        }
        rootPages: allMarkdownRemark(
          limit: 1000
          filter: { fileAbsolutePath: { regex: "/(root)/" } }
        ) {
          edges {
            node {
              fields {
                slug
              }
              frontmatter {
                title
                tags
                published
              }
            }
          }
        }
      }
    `
  )

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

  // Create blog posts pages.
  const posts = result.data.posts.edges
  const publishedPosts = posts.filter((edge) => edge.node.frontmatter.published)
  const unpublishedPosts = posts.filter(
    (edge) => !edge.node.frontmatter.published
  )

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

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

  unpublishedPosts.forEach((post) => {
    createPage({
      path: post.node.fields.slug,
      component: blogPost,
      context: {
        slug: post.node.fields.slug,
      },
    })
  })

  // Extract tag data from query
  const tags = result.data.tagsGroup.group

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

  // Create newsletter archive
  const issues = result.data.issues.edges

  issues.forEach((issue) => {
    createPage({
      path: `/newsletter${issue.node.fields.slug}`,
      component: newsletterTemplate,
      context: {
        slug: issue.node.fields.slug,
      },
    })
  })

  // Set root pages written in Markdown
  const rootPages = result.data.rootPages.edges

  rootPages.forEach((root) => {
    createPage({
      path: root.node.fields.slug,
      component: rootPagesTemplate,
      context: {
        slug: root.node.fields.slug,
      },
    })
  })
}

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

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