problem writing to a counter_cache with update_attribute

I’m sure you read Frederick’s response about the counter_cache being readonly.

The way to properly populate these during a migration is to redeclare the Learner class as an inner-class of the Migration itself, specifying only minimal functionality.

class AddCounterCacheToLearners < ActiveRecord::Migration

class Learner < ActiveRecord::Base

def reset_column_information

  # re-implement reset_column_information functionality here

end

end

def self.up
add_column :learners, :learner_sessions_count, :integer, :default => 0
Learner.reset_column_information
end

def self.down
remove_column :learners, :learner_sessions_count

end
end

Thanks Frederic and Duncan,

FYI: here's the complete migration for the simple test case that adds a counter_cache AND sets the value.

class AddCounterCacheToLearners < ActiveRecord::Migration
   class Learner < ActiveRecord::Base
     has_many :learner_sessions
     def reset_column_information
       # re-implement reset_column_information functionality here
       generated_methods.each { |name| undef_method(name) }
       @column_names = @columns = @columns_hash = @content_columns = @dynamic_methods_hash = @generated_methods = @inheritance_column = nil
     end
   end

   def self.up
     add_column :learners, :learner_sessions_count, :integer, :default => 0
     Learner.reset_column_information
     Learner.find(:all).each do |learner|
       count = learner.learner_sessions.count
       learner.update_attribute(:learner_sessions_count, count)
     end
   end

   def self.down
     remove_column :learners, :learner_sessions_count
   end
end

Or you could use http://rails.lighthouseapp.com/projects/8994/tickets/228 :slight_smile:

Thanks for that pointer Damian. I didnm't know about the class method Model.update_counters.

I've simplified my migration as follows:

class AddCounterCacheToLearners < ActiveRecord::Migration
  def self.up
    add_column :learners, :learner_sessions_count, :integer, :default => 0
    Learner.reset_column_information
    Learner.find(:all).each do |learner|
      change_in_count = learner.learner_sessions.count - learner.learner_sessions_count
      Learner.update_counters(learner.id, :learner_sessions_count => change_in_count)
    end
  end

  def self.down
    remove_column :learners, :learner_sessions_count
  end
end

While this is better than my previous solution it still seems a bit ugly.

I like your proposed patch but it's marked as "wontfix".

In my simplified migration above this section:

    Learner.reset_column_information
    Learner.find(:all).each do |learner|
      change_in_count = learner.learner_sessions.count - learner.learner_sessions_count
      Learner.update_counters(learner.id, :learner_sessions_count => change_in_count)
    end

is equivalent to the suggestions at the end of your patch discussion for a class method something like this:

    Learner.update_counter_cache

I like some of the ideas here, and I've been annoyed by this issue
quite a few times. Did a new ticket get created, or was a consensus
about an approach reached?

- Trevor

No consensus :-/

I think the resolution was "we don't want yet another migration helper" (?).

I like the idea of adding a class method like
Model.reset_counter_cache(:column_name)

I don't think there is a new ticket.

I like that as well. I made a new ticket:

http://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/1211-reset_counter_cache

This is probably something I can work on, unless somebody else is
chomping at the bit.