title: Fetch only the ids from a hasMany in Grails?
body: <p>I know I can do <code>Parent.childId</code> in Grails, but is there anything similar I can do to only load ids (proxies) for every children in a hasMany? I.e., something similar to <code>Parent.childrenIds</code>?</p>
  
  <p>In my case, the hasMany is mapped by a joinTable.</p>