match /books/{bookId} {
      allow get, list, delete;
    }
    match /books/{bookId} {
      allow create:
      if request.resource.data.keys().hasOnly([
      	'title',
        'author',
        'isbn'
      ])
      && request.resource.data.keys().size() == 3
      && request.resource.data['author'] is string
      && request.resource.data['author'].size() > 0
      && request.resource.data['author'].size() < 257
      && request.resource.data['title'] is string
      && request.resource.data['title'].size() > 0
      && request.resource.data['title'].size() < 257
      && request.resource.data['isbn'] is string
      && request.resource.data['isbn'].size() > 0
      && request.resource.data['isbn'].size() < 14;

      allow update:
      if resource.data.diff(request.resource.data).affectedKeys().hasOnly([
              "author",
              "title",
              "isbn"
              ])
           && request.resource.data["author"] is string
           && request.resource.data["author"].size() > 0
           && request.resource.data["author"].size() < 257
           && request.resource.data["title"] is string
           && request.resource.data["title"].size() > 0
           && request.resource.data["title"].size() < 257
           && request.resource.data["isbn"] is string
           && request.resource.data["isbn"].size() > 0
           && request.resource.data["isbn"].size() < 14;
    }