title: How to do a single row query with Android Room
body: <p>How do I make a single row query with Android Room with RxJava? I am able to query for List of items, no issues. Here, I want to find if a specific row exists. According to the docs, looks like I can return Single and check for EmptyResultSetException exception if no row exists.</p>
  
  <p>I can have something like:</p>
  
  <pre><code>@Query("SELECT * FROM Users WHERE userId = :id LIMIT 1")
  Single&lt;User&gt; findByUserId(String userId);
  </code></pre>
  
  <p>How do I use this call? Looks like there is some onError / onSuccess but cannot find those methods on Single&lt;>.</p>
  
  <pre><code>usersDao.findByUserId("xxx").???
  </code></pre>
  
  <p>Any working example will be great!</p>