Update references via Content Migration script

import { isEqual } from 'lodash'
import { defineMigration, set } from 'sanity/migrate'

// ! change these to your values
const title = 'This is an old page title'
const newTitle = 'This is your new page title'
const refType = 'page'

export default defineMigration({
  title: `Change references from "${title}" to "${newTitle}"`,
  // ! change this to your document types
  documentTypes: [ 'page', 'article', 'settings' ],
  migrate: {
    // first we need to define which method we want to use (string, array, object, etc) -> since we need to fetch the old and new doc Ids it is async
    async string(node, path, context) {
      // first configure the correct client and make sure we get the "normalised" IDs (no drafts)
      const client = context.client.withConfig({ perspective: 'previewDrafts' })
      
      let oldReferenceId: string | null = null
      let newReferenceId: string | null = null

      try {
        // fetch the old reference ID from the old title
        const oldReference = await client.fetch(
          `*[_type == "${refType}" && title == "${title}"][0]._id`,
        )
        oldReferenceId = oldReference

        // fetch the new reference ID from the new title
        const newReference = await client.fetch(
          `*[_type == "${refType}" && title == "${newTitle}"][0]._id`,
        )
        newReferenceId = newReference
      } catch (error) {
        console.error('Error fetching documents', error)
      }

      // migrate all document with the old reference to the new reference ID
      if (node === oldReferenceId && !isEqual(path, ['_id'])) {
        return set(newReferenceId)
      }
    },
  },
})