This Rails helper allows simple parsing of params that have originated from ActionView's `date_select` helper method into a `Date` or `DateTime` object in a consistent and clean way.

date_helper.rb

module DateHelper

  
  def date_from_date_select_params(date_params, key)
    string_from_date_select_params(date_params, key).to_date
  end

  def date_time_from_date_time_select_params(date_params, key)
    string_from_date_select_params(date_params, key).to_datetime
  end

  private

    def string_from_date_select_params(params, key)
      date_parts = params.select { |k,v| k.to_s =~ /\A#{key}\([1-6]{1}i\)/ }.values
      date_parts[0..2].join('-') + ' ' + date_parts[3..-1].join(':')
    end

end

date_helper_spec.rb

require "spec_helper"

describe DateHelper do
  describe "#date_from_date_select_params" do
    let(:params) { {"test(1i)" => "2013", "test(2i)" => "10", "test(3i)" => "15"} }
    subject { helper.date_from_date_select_params(params, :test) }

    it { subject.should be_a(Date) }
    it { subject.year.should eq 2013 }
    it { subject.month.should eq 10 }
    it { subject.day.should eq 15 }

    context "extra params provided" do
      let(:extra_params) { params.merge({"test(4i)" => "20"}) }
      subject { helper.date_from_date_select_params(extra_params, :test) }
      it { subject.should be_a(Date) }
      it { subject.strftime("%d/%m/%Y").should eq "15/10/2013" }
    end

    context "params not from date select provided" do
      let(:extra_params) { params.merge({"test(something)" => "test"}) }
      subject { helper.date_from_date_select_params(extra_params, :test) }
      it { subject.should be_a(Date) }
      it { subject.to_s.should_not include "test" }
    end
  end

  describe "#date_time_from_date_time_select_params" do
    let(:params) { {"test(1i)" => "2013", "test(2i)" => "10", "test(3i)" => "15", "test(4i)" => "23", "test(5i)" => "59", "test(6i)" => "59" } }
    subject { helper.date_time_from_date_time_select_params(params, :test) }

    it { subject.should be_a(DateTime) }
    it { subject.year.should eq 2013 }
    it { subject.month.should eq 10 }
    it { subject.day.should eq 15 }
    it { subject.hour.should eq 23 }
    it { subject.second.should eq 59 }
    it { subject.minute.should eq 59 }

    context "extra params provided" do
      let(:extra_params) { params.merge({"test(7i)" => "20"}) }
      subject { helper.date_time_from_date_time_select_params(extra_params, :test) }
      it { subject.should be_a(DateTime) }
      it { subject.strftime("%d/%m/%Y %H:%M:%S").should eq "15/10/2013 23:59:59" }
    end

    context "params not from date select provided" do
      let(:extra_params) { params.merge({"test(something)" => "test"}) }
      subject { helper.date_time_from_date_time_select_params(extra_params, :test) }
      it { subject.should be_a(DateTime) }
      it { subject.to_s.should_not include "test" }
    end
  end
end