Creating a hash in Rails 3 - ruby-on-rails

Question

I have the makings of a method which calculates royalties for ISBNs. It splits sales by sales channel. The royalty rate is determined by the total quantity sold, and the royalty is calculated by multiplying the royalty rate (a percentage) by the total revenue. So the result should be a calculated royalty figure for each sales channel, for each isbn. Forgive what is probably over-commented code.
In the show method of the isbns_controller:
#isbn = Isbn.find(params[:id])
def royalty(isbn)
#royaltiesbychannel = Hash.new()
# Returns all sales for the current isbn, and groups them by channel_id in a hash
# {1 => sale 1, sale 2}, {2 => sale 1, sale 2}
# Then loops through each key-value pair.
#isbn.sales.group_by(&:channel_id).each do |ch_id, sale_array|
# Takes the sales grouped by channel, and totals the quantities and values into two separate variables.
value_total_by_channel = sale_array.sum(&:value)
quantity_total_by_channel = sale_array.sum(&:quantity)
# Gets all the rules for the isbn
#isbn.rules.each do |rule|
# Jumps to the next sales hash unless the channel ids match
next unless rule.channel_id == ch_id
if Range.new(rule.lower,rule.upper).include?(quantity_total_by_channel)
#royaltiesbychannel[ch_id] = value_total_by_channel * rule.rate
end
end
end
end
It's that last line which is giving me a problem. What I want is to produce a hash with the channel ids as the keys, and the calculated royalties as the values. But instead, it's producing a hash with just one key-value pair, in something which looks like this:
{1=>#<BigDecimal:10132a620,'0.875E5',9(36)>}
I suspect there's something wrong with the way I'm creating a new hash at the top of the method, and also with trying to declare the key in the square brackets.
The rule.rate is a percentage expressed as a decimal, e.g. 0.10. The value is an integer (at the moment, at least). Any thoughts on how to generate this hash?
Secondly, what's the best way to iterate through the resultant hash in the view?
Many thanks in advance.
Update - output of .inspect as requested:
{1=>[#<Sale id: 1, isbn_id: 2, quantity: 3000, value: 122000, currency: "", total_quantity: nil, created_at: "2011-05-16 19:52:36", updated_at: "2011-05-22 14:28:33", customer: "WHS", retail_price: nil, discount: nil, channel_id: 1, invoice_date: "2011-02-01", rule_id: nil>, #<Sale id: 2, isbn_id: 2, quantity: 500, value: 3000, currency: "", total_quantity: nil, created_at: "2011-05-19 09:55:00", updated_at: "2011-05-19 09:55:00", customer: "Borders", retail_price: nil, discount: nil, channel_id: 1, invoice_date: nil, rule_id: nil>], 2=>[#<Sale id: 6, isbn_id: 2, quantity: 10, value: 2000, currency: "", total_quantity: nil, created_at: "2011-05-19 10:34:34", updated_at: "2011-05-19 11:21:07", customer: "Bookshop a", retail_price: nil, discount: nil, channel_id: 2, invoice_date: nil, rule_id: nil>, #<Sale id: 7, isbn_id: 2, quantity: 2000, value: 4000, currency: "", total_quantity: nil, created_at: "2011-05-19 10:34:49", updated_at: "2011-05-19 10:34:49", customer: "Bookshop b", retail_price: nil, discount: nil, channel_id: 2, invoice_date: nil, rule_id: nil>]}
Second update: revision to the question:
Thanks for your thoughts so far. It turns out the method is working fine, because the hash generated by #isbn.sales.group_by(&:channel_id) only contains one key-value pair. So my question still stands, but for a different bit of my code: how do I perform a find on the Sales model to produce an array of hashes like {1 => sale 1, sale 2}, {2 => sale 1, sale 2}?
I have tried this horrible thing:
#channelarray = Channel.select(:id).all
#salesbychannelwrong = #channelarray.group_by {|i| Sale.where("channel_id = ?",i).where("isbn_id =?", #isbn)}
#salesbychannel = #salesbychannelwrong.invert
which gives this:
{[#<Channel id: 1>]=>[#<Sale id: 1, isbn_id: 2, quantity: 3000, value: 122000, currency: "", total_quantity: nil, created_at: "2011-05-16 19:52:36", updated_at: "2011-05-22 14:28:33", customer: "WHS", retail_price: nil, discount: nil, channel_id: 1, invoice_date: "2011-02-01", rule_id: nil>, #<Sale id: 2, isbn_id: 2, quantity: 500, value: 3000, currency: "", total_quantity: nil, created_at: "2011-05-19 09:55:00", updated_at: "2011-05-19 09:55:00", customer: "Borders", retail_price: nil, discount: nil, channel_id: 1, invoice_date: nil, rule_id: nil>], [#<Channel id: 2>]=>[#<Sale id: 6, isbn_id: 2, quantity: 10, value: 2000, currency: "", total_quantity: nil, created_at: "2011-05-19 10:34:34", updated_at: "2011-05-19 11:21:07", customer: "Bookshop a", retail_price: nil, discount: nil, channel_id: 2, invoice_date: nil, rule_id: nil>, #<Sale id: 7, isbn_id: 2, quantity: 2000, value: 4000, currency: "", total_quantity: nil, created_at: "2011-05-19 10:34:49", updated_at: "2011-05-19 10:34:49", customer: "Bookshop b", retail_price: nil, discount: nil, channel_id: 2, invoice_date: nil, rule_id: nil>]}
I have also tried
Sale.find_by_isbn_id(:id).group_by(&:channel_id)
which returns nil
and this
Sale.find_by_isbn_id(#isbn).group_by(&:channel_id)
which returns
undefined method `group_by' for #<Sale:0x0000010122df60>
I have the following models:
class Sale
belongs_to :isbn
belongs_to :channel
...
end
class Isbn
has_many :rules
has_many :sales
has_many :channels, :through => :sales
...
end
class Channel
has_many :sales
has_many :rules
...
end
class Rule
belongs_to :isbn
belongs_to :channel
has_many :sales, :through => :isbn
...
end
Thanks again.

Answer 1

Sale.find_by_isbn_id(#isbn).group_by(&:channel_id) => Sale.find_all_by_isbn_id(#isbn).group_by(&:channel_id)
or
Sale.where(:ibn_id => #isbn.id).group_by(&:channel_id)