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Asked: 2026-06-10T16:44:47+00:00

I have an Active Record model object called Event, which has many event_things. I

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I have an Active Record model object called Event, which has many event_things. I want to be able to duplicate the event, so that it gets a new id. I’m using Rails 3.2 and in rails console am able to successfully call

event_copy = event.dup
event_copy.save

However, I also want to duplicate each of the Event’s event_things.

copy = event_thing.dup
copy.event_id = event_copy.id
copy.save

But that gives me this error stack:

NoMethodError: undefined method `yaml' for nil:NilClass
    from /Users/Ed/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1/psych.rb:204:in `dump_stream'
    from /Users/Ed/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1/psych/core_ext.rb:35:in `psych_y'
    from /Users/Ed/.rvm/gems/ruby-1.9.3-p125/gems/activemodel-3.2.6/lib/active_model/dirty.rb:143:in `attribute_change'
    from /Users/Ed/.rvm/gems/ruby-1.9.3-p125/gems/activemodel-3.2.6/lib/active_model/dirty.rb:117:in `block in changes'
    from /Users/Ed/.rvm/gems/ruby-1.9.3-p125/gems/activemodel-3.2.6/lib/active_model/dirty.rb:117:in `map'
    from /Users/Ed/.rvm/gems/ruby-1.9.3-p125/gems/activemodel-3.2.6/lib/active_model/dirty.rb:117:in `changes'
    from /Users/Ed/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/attribute_methods/dirty.rb:23:in `save'
    from /Users/Ed/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/transactions.rb:241:in `block (2 levels) in save'
    from /Users/Ed/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/transactions.rb:295:in `block in with_transaction_returning_status'
    from /Users/Ed/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/connection_adapters/abstract/database_statements.rb:192:in `transaction'
    from /Users/Ed/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/transactions.rb:208:in `transaction'
    from /Users/Ed/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/transactions.rb:293:in `with_transaction_returning_status'
    from /Users/Ed/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/transactions.rb:241:in `block in save'
    from /Users/Ed/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/transactions.rb:252:in `rollback_active_record_state!'
    from /Users/Ed/.rvm/gems/ruby-1.9.3-p125/gems/activerecord-3.2.6/lib/active_record/transactions.rb:240:in `save'
    from (irb):18
    from /Users/Ed/.rvm/gems/ruby-1.9.3-p125/gems/railties-3.2.6/lib/rails/commands/console.rb:47:in `start'
    from /Users/Ed/.rvm/gems/ruby-1.9.3-p125/gems/railties-3.2.6/lib/rails/commands/console.rb:8:in `start'
    from /Users/Ed/.rvm/gems/ruby-1.9.3-p125/gems/railties-3.2.6/lib/rails/commands.rb:41:in `<top (required)>'
    from script/rails:6:in `require'
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1 Answer

  1. Editorial Team

    While I normally don’t advocate using gems liberally, if you have a lot of relations that need to be preserved in the duplication, or find yourself doing these manual duplications a lot, take a look at deep_clonable.

    As for your specific error, try surrounding each line of code with a nil check (one line at a time). I’m sure there’s just some case where you’re ending up with a nil object that you’re overlooking.

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