Rails: how to add items to an instance variable - ruby-on-rails

Question

In my index action I am creating an instance variable like so:
def index
#cards = Card.where(:cardstack_id => params[:cardstack_id])
end
This creates the output for #cards:
[#<Card id: 3, header: "Crazy", body: "Lege deinen Kopf für zwei Minuten auf den Tisch un...", points: 1, cardstack_id: 1, created_at: "2017-06-09 16:41:09", updated_at: "2017-06-13 17:24:29", lifetime: 240>, #<Card id: 4, header: "Böse Zungen", body: "Sprich 20 Minuten in einem starken Dialekt, der un...", points: 3, cardstack_id: 1, created_at: "2017-06-09 16:42:11", updated_at: "2017-06-13 17:26:24", lifetime: 360> ...
What I want to do now is to add for each object a random token created with SecureRandom.uuid.
So my output should look like this:
[#<Card id: 3, header: "Crazy", token: "34985jlskd908tjkls980", body : "..." ...]
How can I achieve this? I guess I have to somehow loop through the array in my controller, create a token for each element and then add it to a new array. However, I don't know how to achieve this.

Answer 1

I guess I have to somehow loop through the array in my controller,
create a token for each element and then add it to a new array.
However, I don't know how to achieve this.
You won't be able to do this and keep a ActiveRecord::Relation object (which is the result of your query); but you could get an array of hashes, where each hash will contain all attributes (and values) for each record, including any new key you need to add, for example:
#cards = #cards.map { |i| i.attributes.symbolize_keys.merge({ token: SecureRandom.uuid }) }
Using your example, this will be the content for #cards:
[
{
:id=>3,
:header=>"Crazy",
:body=>"Lege deinen Kopf für zwei Minuten auf den Tisch un...",
:points=>1,
:cardstack_id=>1,
:created_at=>"2017-06-09 16:41:09",
:updated_at=>"2017-06-13 17:24:29",
:lifetime=>240,
:token=>"fa637bfa-a781-4029-8f60-2763e75d6d5c"
},
{
:id=>4,
:header=>"Böse Zungen",
:body=>"Sprich 20 Minuten in einem starken Dialekt, der un...",
:points=>3,
:cardstack_id=>1,
:created_at=>"2017-06-09 16:42:11",
:updated_at=>"2017-06-13 17:26:24",
:lifetime=>360,
:token=>"2ff962cf-2258-4f2a-8d50-d8a864fb845a"
}
]
Then, you can iterate in your view just like any array, for example:
<% #cards.each do |card| %>
<p>ID: <%= card[:id] %></p>
<p>Header: <%= card[:header] %></p>
...
<p>Token: <%= card[:token] %></p>
<% end %>

Answer 2

It looks like you want to generate a UUID value for each card so that you can use it as a public id value without exposing the db id. Is that correct?
In that case, you shouldn't be doing it here. This should be done in after_initialize.
class Card < ActiveRecord::Base
after_initialize do
self.token ||= SecureRandom.uuid if has_attribute?(:token)
end
end
Use of has_attribute? is necessary here in case you constrain the lookup with select and don't include token in the query.
Make sure you read up on the performance impacts of UUIDs in databases.
I ended up using this pattern for so many things I wrote a simple gem for it.
class Card < ActiveRecord::Base
safe_initialize :token, with: ->{ SecureRandom.uuid }
end