gatsby-node.js

const path = require('path')

module.exports.createPages = async({ graphql, actions }) => {
  const { createPage } = actions
  const blogTemplate = path.resolve(`./src/templates/blog.js`)
  const res = await graphql(`
    query {
      allContentfulBlogPost {
        edges {
          node {
            slug
          }
        }
      }
    }
  `)
  res.data.allContentfulBlogPost.edges.forEach((edge) => {
    createPage({
      component: blogTemplate,
      path: `/blog/${edge.node.slug}`,
      context: {
        slug: edge.node.slug
      }
    })
  })
}