gatsby-node.js

const _ = require(`lodash`)
const path = require(`path`)
const { slash } = require(`gatsby-core-utils`)

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


//   createPage({
//     path: "/using-dsg",
//     component: require.resolve("./src/templates/using-dsg.js"),
//     context: {},
//     defer: true,
//   })
// }


exports.createPages = async ({ actions, graphql }) => {
  const { createPage } = actions
  
  const blogPostTemplate = path.resolve(`src/templates/template-blog-post.js`)
  const tagPagesTemplate = path.resolve(`src/templates/template-tag-page.js`)

  return graphql(
    `
      {
        allMarkdownRemark(
          limit: 1000
          filter: { frontmatter: { draft: { ne: true } } }
        ) {
          edges {
            node {
              fields {
                slug
              }
              frontmatter {
                tags
              }
            }
          }
        }
      }
    `
  ).then(result => {
    if (result.errors) {
      throw result.errors
    }

    // Create blog posts pages.
    result.data.allMarkdownRemark.edges.forEach(edge => {
      createPage({
        path: edge.node.fields.slug, // required
        component: slash(blogPostTemplate),
        context: {
          slug: edge.node.fields.slug,
          highlight: edge.node.frontmatter.highlight,
          shadow: edge.node.frontmatter.shadow,
        },
      })
    })

    // Create tag pages.
    let tags = []
    result.data.allMarkdownRemark.edges.forEach(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: tagPagesTemplate,
        context: {
          tag,
        },
      })
    })

  }) // end of then 
}

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 })
    }
  }
}