title: How to retrieve data from many to many relationship tables with Doctrine
body: <p>Let say I have 3 tables: <code>Book</code>, <code>Author</code> and <code>BookAuthor</code>. </p>
  
  <blockquote>
    <ul>
    <li><code>Book</code> has <code>id</code>, <code>name</code></li>
    <li><code>Author</code> has <code>id</code>, <code>name</code></li>
    <li><code>BookAuthor</code> has <code>id</code>, <code>book</code>_id, <code>author</code>_id</li>
    </ul>
  </blockquote>
  
  <p>I want to find all books of an author, and I know <code>author_id</code>.  Can anyone show me how to do this with <code>Doctrine Query Language</code>?</p>