gatsby-node.js

const path = require("path");

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

    return new Promise(async (resolve, reject) => {
        resolve(
            graphql(query).then((result) => {
                if (result.errors) {
                    console.log(result.errors);
                    reject(result.errors);
                }

                result.data.allMdx.edges.forEach(({ node }) => {
                    createPage({
                        path: `/chapters/${node.parent.name}` || "/",
                        component: path.resolve("./src/layouts/chapter.js"),
                        context: {
                            id: node.id,
                        },
                    });
                });
            })
        );
    });
};

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

    if (node.internal.type === `Mdx`) {
        const parent = getNode(node.parent);

        let value = parent.relativePath.replace(parent.ext, "");

        createNodeField({
            node,
            name: `slug`,
            value: `/chapters/${value}`,
        });

        createNodeField({
            node,
            name: "id",
            value: node.id,
        });

        createNodeField({
            node,
            name: "title",
            value: node.frontmatter.title,
        });
    }
};

const query = `
    {
        allMdx {
            edges {
                node {
                    frontmatter { title }
                    id
                    parent { ... on File { name } }
                }
            }
        }
    }
`;