Saving date form to ruby variable - ruby-on-rails

Question

I'm trying to make a date range form in my rails app, so the user can input two dates, and these dates will post to a query to return results from an API the application is connected to.
My model looks like this: It allows the first date and second date to default to create last week's date range, but it is supposed to accept options to overwrite the default...
class Day
include ActiveModel::Validations
include ActiveModel::Conversion
extend ActiveModel::Naming
attr_accessor :first_day, :second_day
def initialize(attributes = {})
attributes.each do |name, value|
send("#{name}=", value)
end
end
def self.monday(options = {})
if options[:first_day]
return Date.parse(options[:first_day])
else
d = Date.today
seven_days_ago = (d - 7)
seven_days_ago.beginning_of_week
end
end
#defines the end of last week for the query
def self.sunday(options = {})
if options[:second_day]
return Date.parse(options[:second_day])
else
d = Date.today
seven_days_ago = (d - 7)
seven_days_ago.end_of_week
end
end
def persisted?
false
end
end
Form:
<%= form_for #day do |f| %>
<div class="field">
<%= f.label 'Beginning Date' %>
<%= f.datepicker :first_day, :size => 6 %>
<%= f.label 'End Date' %>
<%= f.datepicker :second_day, :size => 6 %>
</div>
<div class="actions">
<%= f.submit 'Submit' %>
</div>
<% end %>
And controller:
def new
#day = Day.new
end
# POST /days
# POST /days.json
def create
#day = Day.new(params[:day])
if #day.valid?
redirect_to root_url
end
end
I am currently accessing the Day.monday and Day.sunday methods in queries that live in some of my controllers. These values always end up being the default, even if the user posts other dates through the form (the idea is to overwrite the default values).
I would prefer a javascript option - the user inputs two dates, they stick to the methods without refreshing, then when the dates are reset it goes back to default.
Thanks for any help!