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The following array ["2", "8", "134", "137", "140"] is generated via user input. The controller action invokes the arrays as follows:

params[:product_ids].each do |product_id|
  @product = Product.where('id = ?', product_id).first
end

Unfortunately when calling the values in the view (for development control purposes)

<% params[:product_ids].each do |t| %>
  <%= t %> <%= @product.id %><br />
<% end %>

is rendering the proper value for t but is then associating it with 140 five times.

2 140
8 140
134 140
137 140
140 140

thus accessing the LAST item of the array and ignoring the key. When this is attempted in the controller:

params[:product_ids].each do |k, product_id|

it is returning Called id for nil, which would mistakenly be 4 -- if you really wanted the id of nil, use object_id

How can the controller be defined to appropriately access the parameter's value?

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3 Answers 3

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2

You are assinging the values in a loop to the same variable, put it outside the loop, and use #map to get values as a Transaction model for all product ids, so:

@transactions = params[:product_ids].map do |product_id|
   [ Transaction.where(product_id: product_id).first ]
end

and then:

<%= @transactions %>
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7 Comments

@Malo. This syntax does generate data. What surprised me is that <%= @products %> returned ["2", #<Product id: 2, struttura_id: 1, [...] ["8", #<Product id: 8, struttura_id: 1, etc. In other words, the value, followed by the object's data. Then if I want to loop through each and create new records @products.each do |product| params[:transaction][:product_id] = product.id @transaction = Transaction.new(params[:transaction] I cannot as this is accessing an array...
@Jerome well, and what did you want to get? =)
@Malo The Product's id... But I believe my reasoning has fallen into a circular trap. It would've been more direct to have gone with params[:product_ids].each do |product_id| params[:transaction][:product_id] @transaction = Transaction.new(params[:transaction] ...
@Jerome what product's did you wish to get?
one transaction per param[:product_id]
|
2

In this piece of code:

params[:product_ids].each do |product_id|
  @product = Product.where('id = ?', product_id).first
end

You're updating @product instance variable n times (where n is size of params[:product_ids] table). At the end, @product instance variable holds Product with id which is last element of params[:product_ids], in your case it's 140. I guess it would be better if you set products array, like this:

@products = Product.where(id: params[:product_ids])

so you could iterate over them:

<% @products.each do |product| %>
  <%= product.id %>
<% end %>
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5 Comments

Is this syntax Product.where(id: params[:product_ids]) correct? I haven't come across it before?
@Jerome it's correct. It generates SQL with IN clause.
this is generating Product Load (2.7ms) SELECT "products".* FROM "products" WHERE "products"."id" IS NULL and only once... (postgresql is db)
@Jerome So your params[:product_ids] is probably nil.
Not really. <%= params[:product_ids] %> returns ` ["2", "8", "134", "137", "140"] `
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When you use

params[:product_ids].each do |product_id|
  @product = Product.where('id = ?', product_id).first
end 
# you set @product = 2
# @product = 8
# ...
# @product = 140  last value of @product is 140

solution

@products = params[:product_ids].map do |p_id|
   {p_id => Product.find_by(id: p_id)}    
end

In your view

<% @products.each do |k, v| %>
  <%= k %> <%= v %><br />
<% end %>
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4 Comments

Product.find_by(p_id) won't work. It should be either Product.find_by(id: p_id) or Product.find_by_id(p_id).
nope, find_by without column name doesn't behave like find_by(id: p_id), at least in 4.1.6.
You are right, I was not looking carefully, it returns first object from DB
... or simply raises an error, if you use postgresql for example.

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