Tips for validating document references in Sanity.io

  validation: Rule => Rule.custom(async ({ _id }) => {
    //count the incoming references from Foo docs
    const referenceCount = await studioClient.fetch(`count(*[_type == 'foo' && references(${_id})])`)
    //Return error if 0 Foo docs reference Bar
    return referenceCount > 0 ? true : 'Document must have at least 1 Foo referencing it'
  }),

import client from "part:@sanity/base/client"

export const studioClient = client.withConfig({apiVersion: '2021-03-25'})

import studioClient from './path/to/studioClient.js'

expected ')' following function arguments