gatsby-node.js

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

exports.onCreateNode = ({ node, actions }) => {
  const { createNodeField } = actions;
  let slug;
  if (node.internal.type === 'MarkdownRemark') {
    if (
      Object.prototype.hasOwnProperty.call(node, 'frontmatter') &&
      Object.prototype.hasOwnProperty.call(node.frontmatter, 'slug')
    ) {
      slug = `/${_.kebabCase(node.frontmatter.slug)}`;
    }
    if (
      Object.prototype.hasOwnProperty.call(node, 'frontmatter') &&
      Object.prototype.hasOwnProperty.call(node.frontmatter, 'title')
    ) {
      slug = `/${_.kebabCase(node.frontmatter.title)}`;
    }
    createNodeField({
      node,
      name: `slug`,
      value: slug,
    })
  }
}

exports.createPages = async ({ graphql, actions, reporter }) => {
    const { createPage } = actions;
    const postPage = path.resolve('src/templates/blog-post.js');
    const tagTemplate = path.resolve('src/templates/tags-list-template.js');

    const result = await graphql(`
      {
        posts: allMarkdownRemark(sort: {frontmatter: {date: DESC}}, limit: 1000) {
          edges {
            node {
              fields {
                slug
              }
              frontmatter {
                title
                category
              }
            }
          }
        }
        tags: allMarkdownRemark(limit: 2000) {
          group(field: {frontmatter: {tags: SELECT}}) {
            fieldValue
          }
        }
      }
    `);
    if (result.errors) {
      console.log(result.errors);
      reporter.panicOnBuild(`Error whil running GraphQL query`);
    }

    const posts = result.data.posts.edges;
    const postsPerPage = 10;
    const numPages = Math.ceil(posts.length / postsPerPage);

    Array.from({ length: numPages }).forEach((_, i) => {
      createPage({
        path: i === 0 ? `/blog` : `/blog/${i + 1}`,
        component: path.resolve("./src/templates/blog-list-template.js"),
        context: {
          limit: postsPerPage,
          skip: i * postsPerPage,
          numPages,
          currentPage: i + 1
        }
      })
    });

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

      createPage({
        path: `blog${edge.node.fields.slug}`,
        component: postPage,
        context: {
          slug: edge.node.fields.slug,
          prev,
          next,
        },
      });
    });

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

  };

  exports.createSchemaCustomization = ({ actions }) => {
    const { createTypes } = actions
    const typeDefs = `
      type frontmatter implements Node {
        cover_image: String!
      }
    `
    createTypes(typeDefs)
  }