gatsby-node.js

const pathPrefixes = {
  blog: 'blog',
  features: 'features',
  authors: 'blog/authors',
  'blog-categories': 'blog/category'
}

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

  if (node.internal.type === `MarkdownRemark`) {
    const fileNode = getNode(node.parent)
    const pathPrefix = pathPrefixes[fileNode.sourceInstanceName]
    const slug = createFilePath({ node, getNode })

    createNodeField({ node, name: `slug`, value: `${slug.replace(/\/$/, '')}` })
    createNodeField({ node, name: `path`, value: `/${pathPrefix}${slug}` })
    createNodeField({ node, name: 'sourceInstanceName', value: pathPrefix })
  }
}

exports.createPages = ({ graphql, actions }) => {
  const { createPage } = actions
  return new Promise((resolve, reject) => {
    graphql(`
      {
        allMarkdownRemark {
          edges {
            node {
              id
              fields {
                path
                slug
              }
              frontmatter {
                templateKey
                category {
                  fields {
                    path
                    slug
                  }
                }
              }
            }
          }
        }
      }
    `).then(result => {
      if (result.errors) {
        console.log(result.errors)
        reject(result.errors)
      }
      result.data.allMarkdownRemark.edges.forEach(({ node }) => {
        const id = node.id
        const pageUrl =
          node.frontmatter.category !== null
            ? `/blog${node.frontmatter.category.fields.slug}${node.fields.slug}/`
            : `${node.fields.path}`
        console.log(pageUrl)

        createPage({
          path: pageUrl,
          component: path.resolve(`./src/templates/${String(node.frontmatter.templateKey)}.js`),
          context: {
            // Data passed to context is available
            // in page queries as GraphQL variables.
            slug: node.fields.slug,
            id
          }
        })
      })
      resolve()
    })
  })
}