gatsby-node.js

const path = require('path');
const { createFilePath } = require('gatsby-source-filesystem')
const { fmImagesToRelative } = require('gatsby-remark-relative-images-v2')

// V1. This onCreateNode Gatsby API call creates a new 'node' or a thing to be able to
// manipulate as needed for the project. This particular piece of code will gather the
// 'slug' data information from each episode ( markdown file as currently implemented)
// so that we can use this to create a new page/ URL name based on the slug. This is
// the first step in an effort to build auto-generation of a new podcast episode capibility.
// ex. episode1.md -> episode1 -> our-page-url/episodes/episode1

// V2. Adding another type of collection type of 'members', as the project has evovled to 
// contain 2 different types of markdown files.

module.exports.onCreateNode = ({ node, actions, getNode  }) => {
  const { createNodeField } = actions;
  fmImagesToRelative(node) // convert image paths for gatsby images

    if(node.internal.type === 'MarkdownRemark'){ 
        //const slug = path.basename(node.fileAbsolutePath, '.md')
        const value = createFilePath({ node, getNode })
        createNodeField({
            name: `slug`,
            node,
            value,
        })

        const parent = getNode(node.parent);
        let collection = parent.sourceInstanceName;
        createNodeField({
            node,
            name: "collection",
            value: collection,
        })
    }

}

// This createPages Gastby API creates new pages based on our source data that is
// provided. It uses the episode page template created in /templates/episode.js,
// markdown slug data for each episode,and the createPage action to create the new page.
module.exports.createPages = async ({ graphql, actions }) => {

    const { createPage } = actions
     //1. Get path to templates
    const episodeTemplate = path.resolve('./src/templates/episode.js')
    //2. Get markdown data, (slugs) to create the new pages based on the slugs
    const res = await graphql(`
        query{
            allMarkdownRemark {
                edges {
                    node {
                        fields {
                            slug
                        }
                    }
                }
            }
        }
    `)

    if(res.errors){
        throw res.errors;
    }

    //3. Dynamically create new pages
    // Future enhancement option: can work on adding previous and next episode capibiltiy
    // https://github.com/GeorgeNance/seperating-markdown-by-folder-example/blob/main/gatsby-node.js
    res.data.allMarkdownRemark.edges.forEach((edge) => {
        createPage({
            component: episodeTemplate,
            path:`/episode/${edge.node.fields.slug}`,
            context: {
                slug: edge.node.fields.slug
            }
        })
    });
}