gatsby-node.js

const _ = require('lodash')
const path = require('path')
const { createFilePath } = require('gatsby-source-filesystem')
const { fmImagesToRelative } = require('gatsby-remark-relative-images-v2')
const { execSync } = require("child_process")

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

  return graphql(`
    {
      allMdx(limit: 1000) {
        edges {
          node {
            id
            fields {
              slug
            }
            frontmatter {
              tags
              templateKey
            }
            internal {
              contentFilePath
            }
          }
        }
      }
    }
  `).then((result) => {
    if (result.errors) {
      result.errors.forEach((e) => console.error(e.toString()))
      return Promise.reject(result.errors)
    }

    const posts = result.data.allMdx.edges

    posts.forEach((edge) => {
      const id = edge.node.id
      const postTemplate = path.resolve(`src/templates/${String(edge.node.frontmatter.templateKey)}.js`)
      createPage({
        path: edge.node.fields.slug,
        tags: edge.node.frontmatter.tags,
        component: `${postTemplate}?__contentFilePath=${edge.node.internal.contentFilePath}`,
        // additional data can be passed via context
        context: {
          id,
        },
      })
    })

    // Tag pages:
    let tags = []
    // Iterate through each post, putting all found tags into `tags`
    posts.forEach((edge) => {
      if (_.get(edge, `node.frontmatter.tags`)) {
        tags = tags.concat(edge.node.frontmatter.tags)
      }
    })
    // Eliminate duplicate tags
    tags = _.uniq(tags)

    // Make tag pages
    tags.forEach((tag) => {
      const tagPath = `/tags/${_.kebabCase(tag)}/`

      createPage({
        path: tagPath,
        component: path.resolve(`src/templates/tags.js`),
        context: {
          tag,
        },
      })
    })
  })
}

exports.onCreateNode = ({ node, actions, getNode }) => {
  const { createNodeField } = actions
  // fmImagesToRelative(node) // convert image paths for gatsby images

  if (node.internal.type === `Mdx`) {
    const value = createFilePath({ node, getNode }).replace(
      /\d{4}-\d{2}-\d{2}-/,
      ''
    )
    createNodeField({
      name: `slug`,
      node,
      value,
    })

    // Modification date from git
    // https://pragmaticpineapple.com/add-updated-at-to-your-gatsby-blog/
    const modificationTime = execSync(
      `git log -1 --pretty=format:%aI ${node.internal.contentFilePath}`
    ).toString()
    actions.createNodeField({
      node,
      name: "modificationTime",
      value: modificationTime,
    })
  }
}

exports.onCreatePage = ({ page, actions }) => {
  // Remove unformatted post pages, see #324
  if (page.path.startsWith('/blog/')) {
    actions.deletePage(page)
  }
}