gatsby-node.js

/**
 * Implement Gatsby's Node APIs in this file.
 *
 * See: https://www.gatsbyjs.org/docs/node-apis/
 */

// You can delete this file if you're not using it

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

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 = ({ graphql, actions }) => {
  const { createPage } = actions;
  const blogPostTemplate = path.resolve(`src/templates/blog-post.js`);
  const tagTemplate = path.resolve("src/templates/tag-page.js")

  return graphql(`
    {
      postsRemark: allMarkdownRemark {
        edges {
          node {
            frontmatter {
              path
              draft
              date
              tags
            }
            fields {
              slug
            }
          }
        }
      }
      tagsGroup: allMarkdownRemark(limit: 2000) {
        group(field: frontmatter___tags) {
          fieldValue
        }
      }
    }
  `).then(result => {
    if (result.errors) {
      return Promise.reject(result.errors)
    }

    const posts = result.data.postsRemark.edges

    // Make blog post pages
    posts
      .filter(({ node }) => !node.frontmatter.draft)
      .forEach(({ node }) => {
        createPage({
          path: node.frontmatter.path,
          component: blogPostTemplate,
          slug: node.fields.slug,
          // context: {},
        })
      })
    
    // 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,
        },
      })
    })

  })
}