Migrate categories in an array field on sanity.io

migrateValues.js

/* eslint-disable no-console */
import client from 'part:@sanity/base/client'

// Run this script with: `sanity exec --with-user-token migrations/migrateValues.js`
//
// This example shows how you may write a migration script that migrates a field value
// on a specific document type.
// This will migrate documents in batches of 100 and continue patching until no more documents are
// returned from the query.
//
// This script can safely be run, even if documents are being concurrently modified by others.
// If a document gets modified in the time between fetch => submit patch, this script will fail,
// but can safely be re-run multiple times until it eventually runs out of documents to migrate.

// A few things to note:
// - This script will exit if any of the mutations fail due to a revision mismatch (which means the
//   document was edited between fetch => update)
// - The query must eventually return an empty set, or else this script will continue indefinitely

// Fetching documents that matches the precondition for the migration.
// NOTE: This query should eventually return an empty set of documents to mark the migration
// as complete
const fetchDocuments = () =>
  client.fetch(`*[_type == 'post' && "guides" in categories][0...100] {_id, _rev, categories}`)

const buildPatches = docs =>
  docs.map(doc => ({
    id: doc._id,
    patch: {
      set: {categories: [...doc.categories, 'guide'].filter(cat => cat !== "guides")},
      // this will cause the migration to fail if any of the documents has been
      // modified since it was fetched.
      ifRevisionID: doc._rev
    }
  }))

const createTransaction = patches =>
  patches.reduce((tx, patch) => tx.patch(patch.id, patch.patch), client.transaction())

const commitTransaction = tx => tx.commit()

const migrateNextBatch = async () => {
  const documents = await fetchDocuments()
  const patches = buildPatches(documents)
  if (patches.length === 0) {
    console.log('No more documents to migrate!')
    return null
  }
  console.log(
    `Migrating batch:\n %s`,
    patches.map(patch => `${patch.id} => ${JSON.stringify(patch.patch)}`).join('\n')
  )
  const transaction = createTransaction(patches)
  await commitTransaction(transaction)
  return migrateNextBatch()
}

migrateNextBatch().catch(err => {
  console.error(err)
  process.exit(1)
})