gatsby-node.js

const path = require("path");
const { createFilePath } = require(`gatsby-source-filesystem`);

exports.createPages = async ({ graphql, actions, reporter }) => {
  const { createPage } = actions;
  const postTemplate = path.resolve(`./src/templates/posts-template.js`);

  const posts_results = await graphql(`
    {
      allMarkdownRemark(
        filter: { frontmatter: { typeKey: { eq: "posts" } } }
        sort: { fields: frontmatter___date, order: DESC }
      ) {
        nodes {
          fields {
            slug
          }

          frontmatter {
            author
          }
        }
      }
    }
  `);

  if (posts_results.errors) {
    reporter.panicOnBuild(
      `There was an error loading posts`,
      posts_results.errors
    );
    return;
  }

  const people_results = await graphql(`
    {
      allMarkdownRemark(
        filter: { frontmatter: { typeKey: { eq: "people" } } }
      ) {
        nodes {
          frontmatter {
            full_name
            email
            avatar {
              childImageSharp {
                fluid {
                  base64
                  aspectRatio
                  src
                  srcSet
                  sizes
                }
              }
            }
          }
        }
      }
    }
  `);

  if (people_results.errors) {
    reporter.panicOnBuild(
      `There was an error loading posts`,
      people_results.errors
    );
    return;
  }

  const people = {};
  people_results.data.allMarkdownRemark.nodes.forEach((person, _) => {
    people[person.frontmatter.email] = {
      name: person.frontmatter.full_name,
      email: person.frontmatter.email,
      avatar: person.frontmatter.avatar,
    };
  });

  const posts = posts_results.data.allMarkdownRemark.nodes;

  if (posts.length > 0) {
    posts.forEach((post, _) => {
      createPage({
        path: post.fields.slug,
        component: postTemplate,
        context: {
          slug: post.fields.slug,
          author: people[post.frontmatter.author],
        },
      });
    });
  }
};

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

  if (
    node.internal.type === `MarkdownRemark` &&
    node.frontmatter.typeKey === `posts`
  ) {
    const value = createFilePath({ node, getNode, basePath: `content/posts` });
    createNodeField({
      node,
      name: `slug`,
      value: `/posts${value}`,
    });
  }
};