Rails ActiveRecord group_by & sum db results for use with Lazy HighCharts

Question

I am completely new to RoR/Ruby and i am using Lazy High Charts gem to generate some purdy charts based on some database information.

I have tried the answers that were provided in a previous question but i am still a bit confused as to how to do this..

I need to sum amount_used, and billed_amount and group by month/year (e.g; Aug/2012)

The end result will be something similar to a dual axis chart with two series "Amount Used", and "Cost".. This information is specific to a certain account_id.

Invoices table

+---------------+--------------+------+-----+---------+----------------+
| Field         | Type         | Null | Key | Default | Extra          |
+---------------+--------------+------+-----+---------+----------------+
| id            | int(11)      | NO   | PRI | NULL    | auto_increment |
| account_id    | int(11)      | YES  |     | NULL    |                |
| invoice_date  | varchar(255) | YES  |     | NULL    |                |
| amount_used   | float        | YES  |     | NULL    |                |
| billed_amount | float        | YES  |     | NULL    |                |
| comments      | text         | YES  |     | NULL    |                |
| created_at    | datetime     | NO   |     | NULL    |                |
| updated_at    | datetime     | NO   |     | NULL    |                |
+---------------+--------------+------+-----+---------+----------------+

Controller Chart Code

@account = Account.find(params[:id])
@invoices = Invoice.where("account_id = #{@account.id}").order("invoice_date DESC")

@h = LazyHighCharts::HighChart.new('area') do |f|
  f.options[:chart][:defaultSeriesType] = "area"
  #Sample dates right now, should be the grouped_by :invoice_date
  f.xAxis( :categories => ['May', 'Jun', 'Jul'] )
  f.yAxis([
    {
      :title => { :text => "Amount Used" }
    },
    {
      :title => { :text => "Cost" },
      :opposite => true
    }
  ])
  #Sample data right now, should be the summed amounts of the :amount_used correpsonding for each above grouped invoice_date
  f.series(:name => "Amount Used", :data => [100,300,500] )
  #Sample data right now, should be the summed amounts of the :billed_amount correpsonding for each above grouped invoice date
  f.series(:name => "Cost", :yAxis => 1, :data => [200,400,600] )
end 

Answer 1

It looks like you have everything in place. Here's how you can pull data from db:

@aggregated_invoices = Invoice.
  where(:account_id => params[:id]).
  order("invoice_date DESC").
  group("invoice_date").
  select("DATE_FORMAT(invoice_date, '%Y-%m-01') AS invoice_date, sum(amount_used) AS amount_used, sum(billed_amount) AS billed_amount")

# Then use these instead of sample data:
@categories = @aggregated_invoices.map {|i| i.invoice_date.strftime("%b/%Y")}
@amount_used_data = @aggregated_invoices.map(&:amount_used)
@billed_amount_data = @aggregated_invoices.map(&:billed_amount)