title: MongoDB referred value not being updated
body: <p>I'm using ExpressJS + MongoDB + TypeScript. Below are the models I have</p>
  
  <hr>
  
  <pre><code>export class Author {
      name: string;
      dob: Date;
  }
  </code></pre>
  
  <hr>
  
  <pre><code>export class Publisher {
      name: string;
      address: string;
  }
  </code></pre>
  
  <hr>
  
  <pre><code>import {Author} from './Author';
  import {Publisher} from './Publisher';
  
  export class Book {
      name: string;
      price: number;
      author: Author;
      publisher: Publisher;
  }
  </code></pre>
  
  <hr>
  
  <p>I've inserted the data as below</p>
  
  <pre><code>let publisher1: Publisher = new Publisher();
  publisher1.name = "Publisher 1";
  publisher1.address = "Amritsar";
  
  let publisher2: Publisher = new Publisher();
  publisher2.name = "Publisher 2";
  publisher2.address = "Bangalore";
  
  let author1: Author = new Author();
  author1.name = "Author 1";
  author1.dob = new Date();
  
  let author2: Author = new Author();
  author2.name = "Author 2";
  author2.dob = new Date();
  
  let book1: Book = new Book();
  book1.name = "Book 1";
  book1.price = 50;
  book1.author = author1;
  book1.publisher = publisher1;
  
  let book2: Book = new Book();
  book2.name = "Book 2";
  book2.price = 100;
  book2.author = author2;
  book2.publisher = publisher2;
  
  let book3: Book = new Book();
  book3.name = "Book 3";
  book3.price = 150;
  book3.author = author1;
  book3.publisher = publisher2;
  </code></pre>
  
  <p>There are 3 collections created i.e. Publisher (2 docs), Author (2 docs) and Books (3 docs).</p>
  
  <p>Now when I update the name of <strong>Author 1</strong> to <strong>Author 5</strong> using the below code, it gets changed in the Author collection. </p>
  
  <pre><code>this.db.collection('Author').findOneAndUpdate({
      name: "Author 1"
  }, {
      $set: {
          name: "Author 5"
      }
  })
  </code></pre>
  
  <p>But when I query Book with name <strong>Book 1</strong> or <strong>Book 3</strong>, it still refers to the name <strong>Author 1</strong> instead of <strong>Author 5</strong></p>
  
  <p>Is there something wrong while referring to documents in the Book collection?</p>