gatsby-node.js

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

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

  const postsTemplate = path.resolve(`./src/templates/posts.js`)
  const postTemplate = path.resolve(`./src/templates/post.js`)
  const tagsTemplate = path.resolve("src/templates/tags.js")

  const result = await graphql(
    `
      {
        allMarkdownRemark(
          filter: { fields: { collection: { eq: "posts" } } }
          sort: { fields: [frontmatter___date], order: DESC }
          limit: 1000
        ) {
          edges {
            node {
              frontmatter {
                title
                path
                tags
              }
            }
          }
        }
      }
    `
  )

  const posts = result.data.allMarkdownRemark.edges

  const postsPerPage = 10
  const numberOfPages = Math.ceil(posts.length / postsPerPage)

  Array.from({ length: numberOfPages }).forEach((_, i) => {
    createPage({
      path: i === 0 ? `/` : `/pages/${i + 1}`,
      component: postsTemplate,
      context: {
        limit: postsPerPage,
        skip: i * postsPerPage,
        numberOfPages,
        currentPage: i + 1,
      },
    })
  })

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

    createPage({
      path: post.node.frontmatter.path,
      component: postTemplate,
      context: {
        previous,
        next,
      },
    })
  })

  let tags = []

  _.each(posts, (edge) => {
    if (_.get(edge, "node.frontmatter.tags")) {
      tags = tags.concat(edge.node.frontmatter.tags)
    }
  })

  tags = _.uniq(tags)

  tags.forEach((tag) => {
    createPage({
      path: `/tags/${_.kebabCase(tag)}/`,
      component: tagsTemplate,
      context: {
        tag,
      },
    })
  })
}

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

  if (node.internal.type === `MarkdownRemark`) {
    createNodeField({
      node,
      name: `collection`,
      value: getNode(node.parent).sourceInstanceName,
    })

    createNodeField({
      node,
      name: `slug`,
      value: node.frontmatter.path,
    })
  }
}