gatsby blog next prev

gatsby-node.js

const path = require(`path`)
const { createFilePath } = require(`gatsby-source-filesystem`)

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

  const blogPost = path.resolve(`./src/templates/blog-post.js`)
  const postsPromise = graphql(
    `
      {
        allMarkdownRemark(
          filter: {
            fields: { collection: { eq: "blog" } }
            frontmatter: { draft: { ne: true } }
          }
          sort: { fields: [frontmatter___date], order: DESC }
          limit: 1000
        ) {
          edges {
            node {
              fields {
                slug
              }
              frontmatter {
                title
              }
            }
          }
        }
      }
    `
  ).then(result => {
    if (result.errors) {
      throw result.errors
    }

    // Create blog posts pages.
    const posts = result.data.allMarkdownRemark.edges

    posts.forEach((post, index) => {
      const previous = index === posts.length - 1 ? null : posts[index + 1].node
      const next = index === 0 ? null : posts[index - 1].node

      createPage({
        path: post.node.fields.slug,
        component: blogPost,
        context: {
          slug: post.node.fields.slug,
          previous,
          next,
        },
      })
    })
  })

  const noteComponent = path.resolve(`./src/templates/blog-post.js`)
  const notesPromise = graphql(
    `
      {
        allMarkdownRemark(
          filter: { fields: { collection: { eq: "notes" } } }
          sort: { fields: [frontmatter___date], order: DESC }
          limit: 1000
        ) {
          edges {
            node {
              fields {
                slug
              }
              frontmatter {
                title
              }
            }
          }
        }
      }
    `
  ).then(result => {
    if (result.errors) {
      throw result.errors
    }

    const notes = result.data.allMarkdownRemark.edges
    notes.forEach((note, index) => {
      const previous = index === notes.length - 1 ? null : notes[index + 1].node
      const next = index === 0 ? null : notes[index - 1].node

      createPage({
        path: "notes" + note.node.fields.slug,
        component: noteComponent,
        context: {
          slug: note.node.fields.slug,
          previous,
          next,
        },
      })
    })
  })

  return Promise.all([notesPromise, postsPromise])
}

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

  if (node.internal.type === `MarkdownRemark`) {
    const value = createFilePath({ node, getNode })

    const parent = getNode(node.parent)

    createNodeField({
      node,
      name: "collection",
      value: parent.sourceInstanceName,
    })
    createNodeField({
      name: `slug`,
      node,
      value,
    })
  }
}