Monkey patch rails 3.2 rake task

Question

I'm trying to make a monkey patch for a rake tasks in Rails 3.2 and I want to implement this in a gem (let's call him my_plugin)

For example, the databases.rake has the following content :

db_namespace = namespace :db do
  # ...
  # desc "Retrieves the charset for the current environment's database"
  task :charset => [:environment, :load_config] do
    config = ActiveRecord::Base.configurations[Rails.env]
    case config['adapter']
    when /mysql/
      ActiveRecord::Base.establish_connection(config)
      puts ActiveRecord::Base.connection.charset
    when /postgresql/
      ActiveRecord::Base.establish_connection(config)
      puts ActiveRecord::Base.connection.encoding
    when /sqlite/
      ActiveRecord::Base.establish_connection(config)
      puts ActiveRecord::Base.connection.encoding
    else
      $stderr.puts 'sorry, your database adapter is not supported yet, feel free to submit a patch'
    end
  end
  # ...
end

And I want to replace the default behaviors by mine :

db_namespace = namespace :db do
  # ...
  # desc "Retrieves the charset for the current environment's database"
  task :charset => [:environment, :load_config] do
    puts 'Here is my gem override'
    config = ActiveRecord::Base.configurations[Rails.env]
    case config['adapter']
    when /mysql/
      ActiveRecord::Base.establish_connection(config)
      puts ActiveRecord::Base.connection.charset
    when /postgresql/
      ActiveRecord::Base.establish_connection(config)
      puts ActiveRecord::Base.connection.encoding
    when /sqlite/
      ActiveRecord::Base.establish_connection(config)
      puts ActiveRecord::Base.connection.encoding
    when /OTHER_ADAPTER/
      puts 'OTHER_ADAPTER_ENCODING'
    else
      $stderr.puts 'sorry, your database adapter is not supported yet, feel free to submit a patch'
    end
  end
  # ...
end

So I write the following code in my_plugin :

File : my_plugin.rb

if defined?(Rake)
  Rake::TaskManager.class_eval do
    def replace_task(task_name, task_scope)
      scope_backup = @scope
      @scope = Rake::Scope.new(task_scope)
      task_name_full = @scope.path_with_task_name(task_name)
      @tasks[task_name_full] = yield
      @scope = scope_backup
    end
  end

  Rake.application.replace_task('charset', 'db') do
    task :charset => [:environment, :load_config] do
      puts 'Here is my gem override'
      config = ActiveRecord::Base.configurations[Rails.env]
      case config['adapter']
      when /mysql/
        ActiveRecord::Base.establish_connection(config)
        puts ActiveRecord::Base.connection.charset
      when /postgresql/
        ActiveRecord::Base.establish_connection(config)
        puts ActiveRecord::Base.connection.encoding
      when /redshift/
        ActiveRecord::Base.establish_connection(config)
        puts ActiveRecord::Base.connection.encoding
      when /sqlite/
        ActiveRecord::Base.establish_connection(config)
        puts ActiveRecord::Base.connection.encoding
      when /OTHER_ADAPTER/
        puts 'OTHER_ADAPTER_ENCODING'
      else
        $stderr.puts 'sorry, your database adapter is not supported yet, feel free to submit a patch'
      end
    end
  end
end

But when i call bundle exec rake db:charset :

** Invoke db:charset (first_time)
** Invoke environment (first_time)
** Execute environment
** Invoke db:load_config (first_time)
** Execute db:load_config
** Execute db:charset
UTF8                                       -> First call from rails default method
Here is my gem override
UTF8                                       -> Second call, my monkey patch
Shutdown completed cleanly

Why there's the first call?

Answer 1

Ok, i find a way to make it work thanks to this post : How to monkey patch a rake task shipped with Rails?

So my code is :

Rake::TaskManager.class_eval do
  def replace_task(task_name, task_scope)
    scope_backup = @scope
    @scope = Rake::Scope.new(task_scope)
    task_name_full = @scope.path_with_task_name(task_name)
    @tasks[task_name_full].clear
    @tasks[task_name_full] = yield
    @scope = scope_backup
  end
end

The default is that this monkey patch is really ugly. But it's work.