Rails habtm extend

bar.rb

class Bar < ActiveRecord::Base
  attr_accessible :rec_type
end

foo.rb

class Foo < ActiveRecord::Base

  module OnePerType
    def insert_record(record, force = true, validate = true)
      puts "called insert record with #{record.inspect} in #{self.class}"
      self.delete(*self.where(:rec_type => record.rec_type).all)
      super(record,force,validate)
    end
  end

  has_and_belongs_to_many :bars, :extend => OnePerType
end

foo_test.rb

require 'test_helper'

class FooTest < ActiveSupport::TestCase

  test "only one bar per type" do
    foo = Foo.create

    foo.bars.insert_record Bar.create(:rec_type => "a")
    foo.bars.insert_record Bar.create(:rec_type => "b")
    foo.bars.insert_record Bar.create(:rec_type => "b")

    foo.bars << Bar.create(:rec_type => "a")
    foo.bars << Bar.create(:rec_type => "b")
    foo.bars << Bar.create(:rec_type => "b")

    assert_equal(2, foo.bars.size, "should have two bars")
  end
end

test_result.txt

Started
called insert record with #<Bar id: 1, rec_type: "a", created_at: "2012-08-24 07:39:10", updated_at: "2012-08-24 07:39:10"> in Array
called insert record with #<Bar id: 1, rec_type: "a", created_at: "2012-08-24 07:39:10", updated_at: "2012-08-24 07:39:10"> in ActiveRecord::Relation
E
Finished in 0.264835 seconds.

  1) Error:
test_only_one_bar_per_type(FooTest):
ArgumentError: wrong number of arguments (0 for 1)
    ../gems/activerecord-3.2.6/lib/active_record/relation.rb:440:in `delete'
    ../test_extend/app/models/foo.rb:6:in `insert_record'
    ../gems/ruby-1.9.2-p0@rails3/gems/activerecord-3.2.6/lib/active_record/associations/collection_proxy.rb:100:in `method_missing'
    ../test_extend/app/models/foo.rb:7:in `insert_record'
    ../test_extend/test/unit/foo_test.rb:8:in `block in <class:FooTest>'

1 tests, 0 assertions, 0 failures, 1 errors, 0 skips