Auto-generating Redirects on Slugs Change

import {defineType, defineField, type Rule, type Slug} from 'sanity'

// Shared validation for our redirect slugs
const slugValidator = (rule: Rule) =>
  rule.required().custom((value: Slug) => {
    if (!value || !value.current) return "Can't be blank"
    if (!value.current.startsWith('/')) {
      return 'The path must start with a /'
    }
    return true
  })

export const redirectType = defineType({
  name: 'redirect',
  title: 'Redirect',
  type: 'document',
  description: 'Redirect for next.config.js',
  fields: [
    defineField({
      name: 'source',
      type: 'slug',
      validation: (rule: Rule) => slugValidator(rule),
    }),
    defineField({
      name: 'destination',
      type: 'slug',
      validation: (rule: Rule) => slugValidator(rule),
    }),
    defineField({
      name: 'permanent',
      type: 'boolean',
    }),
  ],
  // null / false makes it temporary (307)
  initialValue: {
    permanent: true,
  },
})

import {createClient} from '@sanity/client'
import {documentEventHandler} from '@sanity/functions'

export const handler = documentEventHandler(async ({context, event}) => {
  const client = createClient({
    ...context.clientOptions,
    useCdn: false,
    apiVersion: '2025-05-08',
  })

  const {beforeSlug, slug} = event.data

  if (!slug || !beforeSlug) {
    console.log('No slug or beforeSlug')
    return
  }
  if (slug === beforeSlug) {
    console.log('Slug did not change')
    return
  }
  // check if redirect already exists
  const existingRedirect = await client.fetch(
    `*[_type == "redirect" && source.current == "${beforeSlug}"][0]`,
  )
  if (existingRedirect) {
    console.log(`Redirect already exists for source ${beforeSlug}`)
    return
  }
  // check for loops
  const loopRedirect = await client.fetch(
    `*[_type == "redirect" && source.current == "${slug}" && destination.current == "${beforeSlug}"][0]`,
  )
  if (loopRedirect) {
    console.log('Redirect loop detected')
    return
  }
  const redirect = {
    _type: 'redirect',
    source: {
      current: beforeSlug,
    },
    destination: {
      current: slug,
    },
    permanent: true,
  }

  try {
    const res = await client.create(redirect)
    console.log(`🔗 Redirect from ${beforeSlug} to ${slug} was created ${JSON.stringify(res)}`)
  } catch (error) {
    console.log(error)
  }
})

import {defineBlueprint, defineDocumentFunction} from '@sanity/blueprints'

export default defineBlueprint({
  resources: [
    defineDocumentFunction({
      type: 'sanity.function.document',
      name: 'auto-redirect',
      src: './functions/auto-redirect',
      memory: 2,
      timeout: 30,
      event: {
        on: ['publish'],
        filter: 'delta::changedAny(slug.current)',
        projection: '{"beforeSlug": before().slug.current, "slug": after().slug.current}',
      },
    }),
  ],
})