gatsby-node.js

const path = require("path")
const _ = require("lodash")
const { createFilePath } = require(`gatsby-source-filesystem`)


exports.onCreateNode = ({ node, getNode, actions }) => {
  const { createNodeField } = actions
  if (node.internal.type === `MarkdownRemark`) {
    const slug = createFilePath({ node, getNode, basePath: `pages` })
    createNodeField({
      node,
      name: `slug`,
      value: slug,
    })
  }
}

exports.createPages = async ({ graphql, actions }) => {
  const tagTemplate = path.resolve("src/templates/tags.js")
  const { createPage } = actions
  const result = await graphql(`
    query {
      allMarkdownRemark {
        edges {
          node {
            fields {
              slug
            }
            frontmatter {
              tags
            }
          }
        }
      }
      tagsGroup: allMarkdownRemark(limit: 2000) {
        group(field: frontmatter___tags) {
          fieldValue
        }
      }
    }
  `)

  result.data.allMarkdownRemark.edges.forEach(({ node }) => {
    createPage({
      path: `/blog${node.fields.slug}`,
      component: path.resolve(`./src/templates/blog-post.js`),
      context: {
        // Data passed to context is available
        // in page queries as GraphQL variables.
        slug: node.fields.slug,
      },
    })
  })
  // Extract tag data from query
  const tags = result.data.tagsGroup.group
  // Make tag pages
  tags.forEach(tag => {
    createPage({
      path: `/tags/${_.kebabCase(tag.fieldValue)}/`,
      component: tagTemplate,
      context: {
        tag: tag.fieldValue,
      },
    })
  })
}