gatsby-node.js

const path = require(`path`)

exports.createPages = ({ graphql, actions }) => {
  const { createPage } = actions
  return new Promise((resolve, reject) => {
    graphql(`
      {
        allMarkdownRemark {
          edges {
            node {
              frontmatter {
                path
                tags
              }
            }
          }
        }
      }
    `).then((result) => {
      if (result.errors) {
        console.log(result.errors)
      }

      result.data.allMarkdownRemark.edges.forEach(({ node }) => {
        createPage({
          path: node.frontmatter.path,
          component: path.resolve(`./src/templates/blog.js`),
          context: { path: node.frontmatter.path },
        })
      })
      resolve()
    })
  })
}