class GradeScale < ActiveRecord::Base

  # Associations
  belongs_to :gradebook

  # Validations
  validates_presence_of :gradebook_id, :grade_letter, :range_start, :range_end
  validates_numericality_of :range_start, :range_end, :greater_than_or_equal_to => 0, :less_than_or_equal_to => 100
  validates_uniqueness_of :grade_letter, :scope => :gradebook_id
  validate :range_exclusion

private

  def range_exclusion
    ranges = GradeScale.find(:all, :select => "range_start, range_end")
    self.errors.add :range_start, 'lies within an existing range' if ranges.any?{ |r| (r.range_start.to_f..r.range_end.to_f).include?(range_start) }
    self.errors.add :range_end, 'lies within an existing range' if ranges.any?{ |r| (r.range_start.to_f..r.range_end.to_f).include?(range_end) }
  end

end

## Test
require File.dirname(__FILE__) + '/../test_helper'

class GradeScaleTest < ActiveSupport::TestCase

  fixtures :grade_scales

  def test_should_add_error_on_conflicting_ranges
    puts "inside tst"
    grade_scale1 = create(:gradebook_id => 1, :grade_letter => 'A', :range_start => 91.2, :range_end => 100)
    assert grade_scale1.valid?, "grade_scale1 should have been valid #{grade_scale1.errors.full_messages.join(', ')}"
  end

private

  def create(options={})
    GradeScale.create({
      :gradebook_id => 1, :grade_letter => 'A'
    }.merge(options))
  end

end

## Error

1) Failure:
test_should_add_error_on_conflicting_ranges(GradeScaleTest)
[test/unit/grade_scale_test.rb:10:in `test_should_add_error_on_conflicting_ranges'
/Library/Ruby/Gems/1.8/gems/activesupport-2.0.2/lib/active_support/testing/default.rb:7:in `run']:
grade_scale1 should have been valid Range start lies within an existing range, Range end lies within an existing range.
<false> is not true.