Rails 5: ActiveRecord collection index_by

问题

Upgraded app to Rails 5 using the index method. The issue is that it is not incrementing to the next ActiveRecord collection record. The below code below use to work in Rails 4.0. Tried with index_by.

def next_question
  index = campaign.quiz_questions.index self
  campaign.quiz_questions[index + 1]
end

Debugger

(byebug) campaign.quiz_questions.index
*** NoMethodError Exception: undefined method `index' for #<QuizQuestion::ActiveRecord_Associations_CollectionProxy:0x007f80012d71b0>
Did you mean?  index_by

Using index_by

(byebug) index = campaign.quiz_questions.index_by
#<Enumerator: #<ActiveRecord::Associations::CollectionProxy [#<QuizQuestion id: 113, campaign_id: 492, message: "Where did Hullabalooza's freak show manager send H...", created_at: "2016-07-20 20:50:32", updated_at: "2016-07-20 20:50:32">]>:index_by>

Index + 1

(byebug) index + 1
*** NoMethodError Exception: undefined method `+' for #<Enumerator:0x007fc4db445960>

nil

回答1:

changed it to find_index method. Now it's working

def next_question
  index = campaign.quiz_questions.find_index self
  campaign.quiz_questions[index + 1]
end

来源：https://stackoverflow.com/questions/38490650/rails-5-activerecord-collection-index-by