title: Slick 3 Transactions
body: <p>I'm confused by the way the slick 3 documentation describes transactions. I have slick 2 code that looks like this:</p>
  
  <pre><code>def doSomething(???) = DB.withTransaction { implicit session =&gt; 
      userDao.doSomething(???)
      addressDao.doSomething(???)
      contactDao.doSomething(???)
  }
  </code></pre>
  
  <p>How can i span a transaction in slick 3?</p>