ruby on rails - Parent fields are all nil when accessed by child (embedded 1-n) -

I have a 1-N relationship defined:

  class user field: Email, type: string embeds_memory: paper and class paper embedded_in: user end   
 If I try to use the original field (user) from the original (paper):  
  User.all.map (: papers) .flatten.first.user.email   
 Then I get zero: ( < P> Access like this work though ok:  
  User.all .first.papers.first.user.email    
 
 
 A misspelling report on this comment To call a method on a map, you need to use  & amp;  before your symbol.  
 Try:  < P>  User.all.map (& amp;: papers). Flatten.first.user.email