gatsby-node.js

const path = require("path");
const _ = require("lodash");

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

exports.onCreateNode = ({
    node,
    actions,
    getNode
}) => {
    const {
        createNodeField
    } = actions;
    if (node.internal.type === `MarkdownRemark`) {
        const slug = createFilePath({
            node,
            getNode
        });
        const fileNode = getNode(node.parent);
        const source = fileNode.sourceInstanceName;
        const separtorIndex = slug.indexOf("--") ? slug.indexOf("--") : 0;
        const shortSlugStart = separtorIndex ? separtorIndex + 2 : 0;

        if (source !== "parts") {
            createNodeField({
                node,
                name: `slug`,
                value: `${separtorIndex ? "/" : ""}${slug.substring(shortSlugStart)}`
            });
        }
        createNodeField({
            node,
            name: `prefix`,
            value: separtorIndex ? slug.substring(1, separtorIndex) : ""
        });
        createNodeField({
            node,
            name: `source`,
            value: source
        });
    }
};

exports.createPages = ({ graphql, actions }) => {
    const { createPage } = actions;
  
    return new Promise((resolve, reject) => {
      const postTemplate = path.resolve("src/templates/post.jsx");
      const tagTemplate = path.resolve("src/templates/tag.jsx");
      resolve(
        graphql(
          `
            {
              allMarkdownRemark(
                sort: { fields: [fields___prefix], order: DESC }
                limit: 1000
                filter: { frontmatter: { draft: { ne: true } } }
              ) {
                edges {
                  node {
                    id
                    fields {
                      slug
                      prefix
                      source
                    }
                    frontmatter {
                      title
                      tags
                    }
                  }
                }
              }
            }
          `
        ).then(result => {
          if (result.errors) {
            console.log(result.errors);
            reject(result.errors);
          }
  
          const items = result.data.allMarkdownRemark.edges;
  
          /* Cria um lista de tags */
          const tagSet = new Set();
          items.forEach(edge => {
            const {
              node: {
                frontmatter: { tags }
              }
            } = edge;
  
            if (tags && tags !== null) {
              tags.forEach(tag => tagSet.add(tag));
            }
          });
  
          /* Cria as páginas de tag */
          const tagList = Array.from(tagSet);
          tagList.forEach(tag => {
            createPage({
              path: `/tag/${_.kebabCase(tag)}/`,
              component: tagTemplate,
              context: {
                tag
              }
            });
          });
  
          /* Cria a página de posts */
          const posts = items.filter(item => item.node.fields.source === "posts");
          posts.forEach(({ node }, index) => {
            const { slug, source } = node.fields;
            createPage({
              path: slug,
              component: postTemplate,
              context: {
                slug,
                source
              }
            });
          });
        })
      );
    });
  };