title: Querying from list of related in SQLalchemy and Flask
body: <p>I have <code>User</code> which <code>has-one</code> <code>Person</code>. So <code>User.person</code> is a <code>Person</code>. <br/>
  I am trying to get a list of <code>User</code> from a list of <code>Person</code>.</p>
  
  <p>I tried the following:</p>
  
  <pre><code>&gt;&gt;&gt; people = Person.query.filter().limit(3)
  &lt;flask_sqlalchemy.BaseQuery object at 0x111c69bd0&gt;
  
  &gt;&gt;&gt; User.query.filter(User.person.in_(people)).all()
  NotImplementedError: in_() not yet supported for relationships.  For a simple many-to-one, use in_() against the set of foreign key values.
  </code></pre>
  
  <p>What is the best way to get a list of <code>User</code>s where <code>User.person</code> is in that list of <code>people</code>? </p>