gistfile1.rbx

class Report < ActiveRecord::Base
  has_many :report_reasons
  has_many :reasons, :through => :report_reasons

  validates_associated :reasons
end

class Reason < ActiveRecord::Base
  has_many :report_reasons
  has_many :reports, :through => :report_reasons

  validates_presence_of :content
  validates_length_of :content, :within => 3..100
end

## tests (rspec)

    @one_invalid_reason_attribute = {
      :document_id => 1,
      :when => Time.now.utc,
      :reason_attributes => [
        { :content => "mr" }
      ]
    }

  it "should not be created with one invalid associated reason attribute" do
    @report = Report.new(@one_invalid_reason_attribute)
    lambda {@report.save!}.should raise_error(ActiveRecord::RecordInvalid)
    
    Reason.count.should == 0
    # There @report will have one reason, but an invalid flagged one.
    @report.should have(1).reasons
    # Rails bug? @errors={"reasons"=>["is invalid", "is invalid"]}
    @report.should have(1).errors_on(:reasons)
  end