setting and array of params in rails - ruby

Question

A series of objects need to be purchased in a single transaction, however each item must be a different transaction object due to relationship issues.
A confirmation action aims to list each of these items independently. The controller attempts to prepare parameters for viewing each transaction
<% #transactions.each do |transaction| %>
<%= params[:product_id][:product_id] %>
[...]
as follows:
#transactions = params[:product_ids].map do |product_id|
#transaction = Transaction.new
#inventories = Inventory.where(['product_id = ?', product_id]).all
#my_price = my_price
params[:product_id][:product_id] = product_id # sanity check
params[:product_id][:additional_info] = session[:additional_info]
params[:product_id][:rate] = #inventories.map(&#my_price).inject(0, :+)
end
#sub_total = #transactions.params[:product_id][:rate].sum
However undefined method []= for nil:NilClass is generated when building the params for each product_id. This command is obviously mistaken. [The approach could also be inefficient/ineffective...]

Answer 1

I believe you don't really mean params[:product_id][:product_id], but rather params[product_id][:product_id], since :product_id is a symbol, not a variable.
When setting a new hash in the hash, you need to first define it as such:
params[product_id] = {}
params[product_id][:product_id] = product_id
# ...
This should resolve the undefined method []= for nil:NilClass. I guess you will encounter some more problems (like #inventories.map(&#my_price)) after you fix this one though...
With some guesswork, I guess a code which does what you want will look something like this:
#transactions = params[:product_ids].map do |product_id|
transaction = Transaction.new
transaction.product_id = product_id # sanity check
transaction.additional_info = session[:additional_info]
transaction.rate = Inventory.where(['product_id = ?', product_id]).sum(:my_price)
transaction
end
#sub_total = #transactions.map(&:rate).sum
And the view would be something like this:
<% #transactions.each do |transaction| %>
<%= transaction.product_id %>
[...]