如何使用graphql对mongoose查询进行验证

我需要检查数据库中是否存在数据。我正在使用graphql和mongoose

这是我的graphql对象：

addBook: {
        type: BookType,
        args: {
            name: { type: new GraphQLNonNull(GraphQLString) },
            genre: { type: new GraphQLNonNull(GraphQLString) },
            authorid: { type: new GraphQLNonNull(GraphQLString) }
        },
        resolve(parent, args){
            let book = new Book({
                name: args.name,
                genre: args.genre,
                authorid: args.authorid
            });
            return book.save();
        }
    },
updateBook: {
        type: BookType,
        args: {
            name: { type: new GraphQLNonNull(GraphQLString) },
            updateName: { type: new GraphQLNonNull(GraphQLString) }
        },
        resolve(parent, args){
            let book = Book.findOneAndUpdate({name: args.name}, {name: args.updateName}, {new: true});
            return book.exec();
        }
    },
deleteBook: {
        type: BookType,
        args: {
            name: { type: new GraphQLNonNull(GraphQLString) }
        },
        resolve(parent, args){
            let book = Book.findOneAndDelete({name: args.name});
            return book.exec();
        }
    }

所有这些都成功地在MongoDB数据库中添加、更新和删除。但我不知道如何首先验证数据是否存在。当我尝试在一本不存在的书上运行更新时，GraphiqlUI抛出null

{
  "data": {
    "updateBook": null
  }
}

我怎样才能检查这个？谢谢大家!