title: How to define a slick joinCondition
body: <p>In the scaladays 2013 talk <a href="http://www.parleys.com/play/51c2e20de4b0d38b54f46243/chapter55/agenda" rel="nofollow">http://www.parleys.com/play/51c2e20de4b0d38b54f46243/chapter55/agenda</a> it talks about "joinCondition" </p>
  
  <p>For example:</p>
  
  <pre><code>implicit def autojoin1 = joinCondition[Sites,Devices](_.id === _.siteId)
  implicit def autojoin2 = joinCondition[Devices,Computers](_.computerId === _.id)
  sites.autoJoin(devices).further(computers)
    : Query[_,(Site,Computer)]
  sites.autoJoin(devices).autoJoinVia(computers)(_._2)
   : Query[_,((Site,Device),Computer)]
  </code></pre>
  
  <p>I'm very new to scala, and can't figure out what joinCondition is, I can't find any method or anything named that in slick(1.0.0) and can't get it to work, what is it?</p>