Patch Sanity documents from one dataset to another

patch.ts

// Example of how to patch documents in a dataset with data from another dataset
// using the Sanity client and transactions. More info: https://www.sanity.io/docs/transactions
import {createClient} from '@sanity/client'

// The 'from' dataset
const source = createClient({
  projectId: 'rwmuledy',
  dataset: 'production',
  useCdn: false,
  token: 'skseugwsW...',
})

// The 'to' dataset, reuse the config from the source dataset but change the
// dataset. Can also use a different project, token etc of course.
const destination = createClient({
  ...source.config(),
  dataset: 'other',
})

// Max size of a transaction we will create, 3.5MB
const MAX_SIZE = 3500000

const run = async () => {
  // Query the source dataset and build up a transaction of createIfNotExists
  // and patch mutations

  let transaction = destination.transaction()

  // Get all documents with a title from the source dataset
  // Change this query to match your needs
  const result = await await source.fetch(`*[ defined(title) ] {_id, _type, title}`)

  for (const row of result) {
    // Make sure the document exists in the destination dataset, that is why
    // we included _type in the query projection
    transaction.createIfNotExists(row)
    // Patch the document in the other dataset with the title from the source
    // dataset, in case the document already existed
    transaction.patch(row._id, {
      set: {title: row.title}, // Also change this to match your needs
    })

    // If the transaction built up so far is larger than the MAX_SIZE, commit
    // early to avoid the transaction getting too large (max 4MB)
    const txSize = Buffer.byteLength(JSON.stringify(transaction.toJSON()))
    if (txSize >= MAX_SIZE) {
      const result = await transaction.commit()
      console.log(result)
      // Start a new transaction for the next batch
      transaction = destination.transaction()
    }
  }

  // Commit the transaction, which will create the documents and/or patch them
  // in the destination dataset. 
  transaction.commit().then(console.log)
}

// Just to get around the top-level await
run()