gatsby-node.js

const path = require("path")

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

  if (node.internal.type === "MarkdownRemark") {
    const slug = path.basename(node.fileAbsolutePath, ".md")
    createNodeField({
      node,
      name: `slug`,
      value: slug,
    })
  }
}

module.exports.createPages = async ({ graphql, actions }) => {
  const { createPage } = actions
  const blogTemplatePath = path.resolve(`src/templates/BlogTemplate.js`)
  const result = await graphql(`
    query {
      allMarkdownRemark {
        edges {
          node {
            fields {
              slug
            }
          }
        }
      },
      allContentfulBlogPosts {
          edges {
              node {
                  slug
              }
          }
      }
    }
  `)
  result.data.allMarkdownRemark.edges.forEach(({ node }) => {
    createPage({
      path: `/blog/${node.fields.slug}`,
      component: blogTemplatePath,
      context: {
        slug: node.fields.slug,
      },
    })
  })
  result.data.allContentfulBlogPosts.edges.forEach(({ node }) => {
    createPage({
      path: `/blog/${node.slug}`,
      component: blogTemplatePath,
      context: {
        slug: node.slug,
      },
    })
  })
}