What's the new before_create in Rails 4? -

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i tried using before_create:

class star < activerecord::base before_create :add_to_total_stars

post load (9.7ms) select "posts".* "posts" "posts"."id" = ? order "posts"."id" asc limit 1 [["id", 1]] (1.0ms) rollback transaction nomethoderror: undefined method `+' nil:nilclass

but can see i'm getting error.

what's new before_create in rails 4?

edit:

class star < activerecord::base   before_create :add_to_total_stars    belongs_to :starable, :polymorphic => true    protected    def add_to_total_stars     if [post].include?(starable.class)       self.starable.update_column(:total_stars, starable.total_stars + self.number)     end   end end  nomethoderror: undefined method `+' nil:nilclass    /home/alex/rails/rating/app/models/star.rb:10:in `add_to_total_stars'  /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-4.0.0/lib/active_support/callbacks.rb:377:in `_run__956917800__create__callbacks'    /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-4.0.0/lib/active_support/callbacks.rb:80:in `run_callbacks'  /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-4.0.0/lib/active_record/callbacks.rb:303:in `create_record'   /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-4.0.0/lib/active_record/timestamp.rb:57:in `create_record'    /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-4.0.0/lib/active_record/persistence.rb:466:in `create_or_update'  /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-4.0.0/lib/active_record/callbacks.rb:299:in `block in create_or_update'   /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-4.0.0/lib/active_support/callbacks.rb:383:in `_run__956917800__save__callbacks'  /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-4.0.0/lib/active_support/callbacks.rb:80:in `run_callbacks'  /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-4.0.0/lib/active_record/callbacks.rb:299:in `create_or_update'    /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-4.0.0/lib/active_record/persistence.rb:106:in `save'  /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-4.0.0/lib/active_record/validations.rb:51:in `save'   /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-4.0.0/lib/active_record/attribute_methods/dirty.rb:32:in `save'   /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-4.0.0/lib/active_record/transactions.rb:270:in `block (2 levels) in save'     /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-4.0.0/lib/active_record/transactions.rb:326:in `block in with_transaction_returning_status'   /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract/database_statements.rb:202:in `block in transaction'     /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract/database_statements.rb:210:in `within_new_transaction'   /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract/database_statements.rb:202:in `transaction'  /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-4.0.0/lib/active_record/transactions.rb:209:in `transaction'  /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-4.0.0/lib/active_record/transactions.rb:323:in `with_transaction_returning_status'    /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-4.0.0/lib/active_record/transactions.rb:270:in `block in save'    /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-4.0.0/lib/active_record/transactions.rb:281:in `rollback_active_record_state!'    /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-4.0.0/lib/active_record/transactions.rb:269:in `save'     (irb):5    /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/railties-4.0.0/lib/rails/commands/console.rb:90:in `start'     /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/railties-4.0.0/lib/rails/commands/console.rb:9:in `start'  /home/alex/.rvm/gems/ruby-1.9.3-p0/gems/railties-4.0.0/lib/rails/commands.rb:64:in `<top (required)>'  bin/rails:4:in `require'   bin/rails:4:in `<main>'1.9.3-p0 :006 > ^c 1.9.3-p0 :006 >  alex@alex-k43u:~/rails/rating$ rails c


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