title: Create a doctrine repository class without an entity
body: <p>I'm currently in a situation where I need to create a <code>Repository</code> class which would contain multiple financial statistic queries. The queries are not exactly tied up with one <code>Entity</code> but rather with multiple <code>Entities</code> and will select specific data from the database, based on various some conditions. </p>
  
  <p>Having said that, I'm looking for a way to create a <code>Repository</code> class (i.e. <code>StatisticsRepository</code>) which is not associated with an <code>Entity</code> at all, so I could store the queries there. Simply creating that repository doesn't seem to be working. I'm guessing I probably need to create a service of some kind that loads this repo class? Is this correct, and if so is there an example I'm missing in the Symfony/Doctrine docs?</p>