setting and array of params in rails

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...]

Uri Agassi · Accepted Answer · 2015-01-04 13:26:55Z

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 %>
[...]

edited Jan 4, 2015 at 13:26

answered Jan 4, 2015 at 13:19

Uri Agassi

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7 Comments

Jerome Over a year ago

Yes, that's correct, I did mean params[product_id][...] and had tried that with unhappy result. Your answer did resolve the indefined method. However in the view it returns undefined local variable or method "product_id"

Uri Agassi Over a year ago

the variable product_id comes from params[:product_ids].map do |product_id|. In the view there is no product_id variable, only transaction variable (from @transactions.each do |transaction|)

Jerome Over a year ago

We crossed paths asynchronously! posted without seeing edit... However undefined method 'product_id' for #<BigDecimal

Uri Agassi Over a year ago

@Jerome in your original code, the @transactions array contains a list of the rate values (the return value of the last line of the map block). I suggest you should check all my suggestion, and see if it suits you better.

Jerome Over a year ago

I see what I missed and where I got sidetracked. Working on your suggestion!

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