title: Returning a list containing multiple entity types in odata v4 (similar to $all)
body: <p>I find myself needing to create an action using odata v4 (the Web Api 2 implementation) that can return either a list containing multiple different entity types OR an action that returns an object that contains many entity types.</p>
  
  <p>However if I create an action returning a List I get an error indicating that all items in the list must be the same type (or derive from a common type).  Now I am assuming that means derive from a common type registered in the entity data model because they do all inherit from object.</p>
  
  <p>If I create a type to nest the various entity types I want to return in, the object that is returned has no data (my guess is because the contents are entity types it is trying to be helpful and leave them as navigation properties or something but that isn't what I need).</p>
  
  <p>As I was digging around trying to figure out how to register the action in the model I came across the $all endpoint (which doesnt appear to work in the web api 2 implementation but it is possible my custom stuff has broken it as well) <a href="http://docs.oasis-open.org/odata/odata/v4.0/errata03/os/complete/part2-url-conventions/odata-v4.0-errata03-os-part2-url-conventions-complete.html#_Toc453752355" rel="nofollow noreferrer">http://docs.oasis-open.org/odata/odata/v4.0/errata03/os/complete/part2-url-conventions/odata-v4.0-errata03-os-part2-url-conventions-complete.html#_Toc453752355</a>
  however I dont have any clue how to do something similar from an action.</p>
  
  <p>i am hoping it is as easy as </p>
  
  <pre><code>actionConfig.ReturnsCollectionOfTypelessGoo() 
  </code></pre>
  
  <p>but i am willing to jump through hoops if that is necessary :)</p>