gatsby-node.js

const _ = require("lodash")
const path = require("path")

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

  return new Promise((resolve, reject) => {
    const pages = []
    const blogPost = path.resolve("src/templates/blog-post.js")
    const tagPages = path.resolve("src/templates/tag-page.js")
    graphql(
      `
        {
          allMarkdownRemark(
            limit: 1000
            filter: { frontmatter: { draft: { ne: true } } }
          ) {
            edges {
              node {
                fields {
                  slug
                }
                frontmatter {
                  tags
                }
              }
            }
          }
        }
      `
    ).then((result) => {
      if (result.errors) {
        console.log(result.errors)
        resolve()
        // reject(result.errors);
      }

      // Create blog posts pages.
      _.each(result.data.allMarkdownRemark.edges, (edge) => {
        createPage({
          path: edge.node.fields.slug, // required
          component: blogPost,
          context: {
            slug: edge.node.fields.slug,
          },
        })
      })

      // Tag pages.
      let tags = []
      _.each(result.data.allMarkdownRemark.edges, (edge) => {
        if (_.get(edge, "node.frontmatter.tags")) {
          tags = tags.concat(edge.node.frontmatter.tags)
        }
      })
      tags = _.uniq(tags)
      tags.forEach((tag) => {
        const tagPath = `/tags/${_.kebabCase(tag)}/`
        createPage({
          path: tagPath,
          component: tagPages,
          context: {
            tag,
          },
        })
      })

      resolve()
    })
  })
}

//exports.postBuild = require('./post-build')

// Add custom url pathname for blog posts.
exports.onCreateNode = ({ node, actions, getNode }) => {
  const { createNodeField } = actions

  if (node.internal.type === `File`) {
    const parsedFilePath = path.parse(node.absolutePath)
    const slug = `/${parsedFilePath.dir.split("---")[1]}/`
    createNodeField({ node, name: `slug`, value: slug })
  } else if (
    node.internal.type === `MarkdownRemark` &&
    typeof node.slug === "undefined"
  ) {
    const fileNode = getNode(node.parent)
    createNodeField({
      node,
      name: `slug`,
      value: fileNode.fields.slug,
    })
    if (node.frontmatter.tags) {
      const tagSlugs = node.frontmatter.tags.map(
        (tag) => `/tags/${_.kebabCase(tag)}/`
      )
      createNodeField({ node, name: `tagSlugs`, value: tagSlugs })
    }
  }
}