gatsby-node.js

const _ = require('lodash')
const path = require('path')
const { createFilePath } = require('gatsby-source-filesystem')
const { fmImagesToRelative } = require('gatsby-remark-relative-images')
const createPaginatedPages = require('gatsby-paginate')

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

  return graphql(`
  {
    allMarkdownRemark(limit: 1000, sort: { order: DESC, fields: [frontmatter___date] }) {
      edges {
        node {
          excerpt(pruneLength: 400)
          id
          fields {
            slug
          }
          frontmatter {
            title
            tags
            templateKey
            date(formatString: "MMMM DD, YYYY")
          }
        }
      }
    }
  }
  `).then(result => {
    if (result.errors) {
      result.errors.forEach(e => console.error(e.toString()))
      return Promise.reject(result.errors)
    }

    const postsAndPages = result.data.allMarkdownRemark.edges

    // Post pages:
    let posts = []
    // Iterate through each post/page, putting all found posts (where templateKey = article-page) into `posts`
    postsAndPages.forEach(edge => {
      if (_.isMatch(edge.node.frontmatter, {'templateKey': 'blog-post'})) {
        posts = posts.concat(edge)
      }
    })

    createPaginatedPages({
      edges: posts,
      createPage: createPage,
      pageTemplate: 'src/templates/blog-index.js',
      pageLength: 5, // This is optional and defaults to 10 if not used
      pathPrefix: 'blog', // This is optional and defaults to an empty string if not used
      context: {}, // This is optional and defaults to an empty object if not used
    })

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

    // Tag pages:
    let tags = []
    // Iterate through each post, putting all found tags into `tags`
    postsAndPages.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 === `MarkdownRemark`) {
    const value = createFilePath({ node, getNode })
    createNodeField({
      name: `slug`,
      node,
      value,
    })
  }
}