gatsby-node.js

// @ts-check
const path = require(`path`);
const _ = require('lodash');
const { createFilePath } = require(`gatsby-source-filesystem`);

exports.onCreateWebpackConfig = ({ actions }) => {
  actions.setWebpackConfig({
    resolve: {
      alias: {
        src: path.resolve(__dirname, 'src'),
      },
    },
  });
};

exports.onCreateNode = ({ node, getNode, actions }) => {
  const { createNodeField } = actions;
  if (node.internal.type === `MarkdownRemark`) {
    const slug = createFilePath({ node, getNode, basePath: `pages` });
    createNodeField({
      node,
      name: `slug`,
      value: slug,
    });
  }
};

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

  const postTemplate = path.resolve(`./src/templates/blog-post.js`);
  const tagTemplate = path.resolve('src/templates/tags.js');

  // filter: get all posts not in drafts folder.
  // filter: { fields: { slug: { regex: "/^((?!/drafts/).)*$/" } } }
  const result = await graphql(`
    query {
      allMarkdownRemark(
        sort: { fields: [frontmatter___date], order: DESC }
        limit: 1000
      ) {
        edges {
          node {
            fields {
              slug
            }
            frontmatter {
              tags
              title
              type
            }
          }
        }
      }
      tagsGroup: allMarkdownRemark(limit: 2000) {
        group(field: frontmatter___tags) {
          fieldValue
        }
      }
    }
  `);

  if (result.errors) {
    reporter.panicOnBuild(`Error while running GraphQL query.`);
    throw result.errors;
  }

  // Create blog posts pages.
  const posts = result.data.allMarkdownRemark.edges;

  posts.forEach((post, index) => {
    const previous = index === posts.length - 1 ? null : posts[index + 1].node;
    const next = index === 0 ? null : posts[index - 1].node;

    const { slug } = post.node.fields;

    // if (node.frontmatter.type !== 'post') {
    //   return;
    // }
    createPage({
      path: slug,
      component: postTemplate,
      context: {
        // Data passed to context is available
        // in page queries as GraphQL variables.
        slug,
        previous,
        next,
      },
    });
  });

  // Extract tag data from query
  const tags = result.data.tagsGroup.group;
  // Make tag pages
  tags.forEach(tag => {
    createPage({
      path: `/tags/${_.kebabCase(tag.fieldValue)}/`,
      component: tagTemplate,
      context: {
        tag: tag.fieldValue,
      },
    });
  });
};