gatsby-node.js

const path = require('path');
const { createFilePath } = require('gatsby-source-filesystem');
const { graphql } = require('gatsby');

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

  return graphql(`
    {
      site {
        siteMetadata {
          languages {
            langs
          }
        }
      }
      markdownRemark {
        frontmatter {
          heading
        }
      }
      allMarkdownRemark(sort: { frontmatter: { date: DESC } }, limit: 1000) {
        edges {
          node {
            id
            fields {
              slug
              langKey
              tagSlugs {
                tag
                link
              }
            }
            frontmatter {
              id
              date
              path
              tags
              templateKey
              lang
              title
              heading
            }
          }
        }
      }
    }
  `).then(result => {
    if (result.errors) {
      result.errors.forEach(e => console.error(e.toString()));
      return Promise.reject(result.errors);
    }

    const posts = result.data.allMarkdownRemark.edges;

    posts.forEach(edge => {
      const id = edge.node.id;
      createPage({
        path: edge.node.fields.slug,
        component: path.resolve(
          `src/templates/${String(edge.node.frontmatter.templateKey)}.jsx`
        ),
        // additional data can be passed via context
        context: {
          id,
        },
      });
    });
  });
};