gatsby-node.js

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

exports.onCreateNode = ({ node, getNode , actions}) => {
    const { createNodeField } = actions
    if (node.internal.type === "MarkdownRemark"){
        const slug = createFilePath({node, getNode, basePath: 'content'})

        createNodeField({
            node,
            name: 'slug',
            value: slug
        })
    }
}


exports.createPages = async ({ graphql, actions }) => {
    const { createPage } = actions
    const result = await graphql(`
        {
            postsRemark: allMarkdownRemark {
                edges {
                    node {
                        fields {
                            slug
                        }
                    }
                }
            }

            tagsGroup: allMarkdownRemark(limit: 2000) {
                group(field: frontmatter___tags) {
                    fieldValue
                }
            }
        }
    `)

    const posts = result.data.postsRemark.edges

    posts.forEach(({ node })=> {
        createPage({
            path: node.fields.slug,
            component: path.resolve('./src/templates/project.js'),
            context: {
                slug: node.fields.slug,
            },
        })
    });

    const tags = result.data.tagsGroup.group

    tags.forEach(tag => {
        createPage({
            path: `/tags/${_.kebabCase(tag.fieldValue)}/`,
            component: path.resolve('./src/templates/tag.js'),
            context: {
                tag: tag.fieldValue,
            },
        })
    })
}