code: @View(name = "by_userId", map = "function(doc) { if(doc.token && doc.userId) { emit(doc.userId, doc) } }")
      public List<CouchDbGoogleAuthenticatorToken> findByUserId(final String userId) {
          return queryView("by_userId", userId);
      }
docs: Find tokens by user id.
  
  @param userId user id to search for
  @return tokens belonging to use id