title: How to implement custom model manager in sonata admin
body: <p>I have a entity in my symfony/sonata application which is not persisted via doctrine orm. Instead i would like to fill the data for these entities on demand by calling an api ... 
  How can i connect this custom managed entity with my existing model which is managed by doctrine orm?
  Is there a way to exchange the doctrine managing part with my custom api calls? I know there are some repository functions like findAll() findBy() and so on ... is the solution to overwrite this functions?</p>
  
  <p>Another approaches?</p>
  
  <p>Thanks</p>