HistoricalParameter

System and models for working with historically changing parameters.

To install add the following line to your Gemfile:

gem 'historical_parameter', :git => 'git://github.com/wise-home/historical_parameter.git'

You will need to isert the following javascript into your application.js to use the view helpers:

//= require acts_as_historical_parameter

To add a migration for the table used to store historical data use this rake command:

rake historical_parameter_rails_engine:install:migrations

class IceCream << ActiveRecord::Base
  # Enable a historical parameter price with id 1
  acts_as_historical_parameter :price, 1

  def get_sales_for_period(period_start, period_end)
    # Do some magic to load # of icecreams of this type
    # sold in the given period
  end

  def get_earnings_for_period(period_start, period_end)
    # Use block sumation to calculate
    price_sum do |period_start, period_end, price|
      # Multiply current price by # of icecreams sold
      get_sales_for_period(period_start, period_end) * value
    end
  end
end

# Load income from first ice for year to date.
IceCream.find(1).get_earnings_for_period(Time.zone.now.beginning_of_year, Time.zone.now)

There are helpers to easilly create a form that allows editing of historical parameters for a model. First if you need to create a form with historical editing use the historical_form_for helper instead of a standard form_for. This will setup the correct builder, this means a form for editing the IceCreams from before will look like:

<%= historical_form_for(@ice_cream) do |f| %>
  <!-- Fields for other attributes ... -->
  <%= f.historical_form_for :price %>
  <%= f.new_history_value_button :price %>
<% end %>

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