Sanity unique e-mail field

unique-email-field.ts

defineField({
  name: 'email',
  title: 'Email',
  type: 'string',
  readOnly: ({document}) => document?.origin === 'Checkin',
  description: 'Can only be changed in Checkin if the origin is "Checkin".',
  validation: Rule => Rule.required().email().custom(async (email: any, context: any) => {
    const response = await client.fetch(`*[_type == "user" && email == $email && !(_id in [$draftId, $id])]`, {email, draftId: context.document._id, id: context.document._id.replace('drafts.', '')});
    if (response?.length > 0) {
      return 'Email already in use';
    }
    return true;
  }),
  group: 'userInformation',
}),