gatsby-node.js

const path = require("path")

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

  //the query below allows to get an array with all the topics (mentioned only once without repetitions)
  const result = await graphql(`
    query GetTopics {
      allContentfulBlog {
        distinct(field: topics)
      }
    }
  `)
  //console.log(result)

  //for each topic a page is created using the topic-template.js file as a base
  result.data.allContentfulBlog.distinct.forEach(topic => {
    //const topicSlug = slugify(topic, { lower: true })
    //createPage is a function taking an object as a parameter containing path, component, context
    createPage({
      path: `/blogs/${topic}`,
      component: path.resolve(`src/templates/topic-template.js`),
      context: {
        topic: topic,
      },
    })
  })
}