Combine API data with local data in Rails - ruby-on-rails-3

Question

I am working with the GoCardless API in my Rails 3 application. I have a subscription model which has a resource_id column which matches the id of the remote record.
I am trying to get extra information for a local subscription record from the API.
Subscription Index View
<% #subscriptions.each do |subscription| %>
<tr>
<td><%= subscription.resource_id %></td>
<td><%= subscription.resource_type %></td>
<td><%= subscription.signature %></td>
<td><%= subscription.state %></td>
<td><%= #gocardless.next_interval_start %></td>
<td><%= link_to 'Show', subscription %></td>
<td><%= link_to 'Edit', edit_subscription_path(subscription) %></td>
<td><%= link_to 'Destroy', subscription, method: :delete, data: { confirm: 'Are you sure?' } %></td>
</tr>
<% end %>
Subscription Controller
def index
#subscriptions = Subscription.all
#gocardless = GoCardless::Merchant.find("XXXXXXXXXX").subscriptions
respond_to do |format|
format.html # index.html.erb
format.json { render json: #subscriptions }
end
end
As you can see I'm using the following line to retrieve the next interval start date
<%= #gocardless.next_interval_start %>
This doesn't work and returns nil. However, if I change it to the following all records show the value from the first record from the API.
<%= #gocardless.first.next_interval_start %>
According to the GoCardless API documentation you can lookup a subscription using the following:
GoCardless::Subscription.find("XXXXXXXXXX") # => #<GoCardless::Subscription ...>
So, my question. How do I pass the current subscription resource_id to the API so that I can view the next_internal_start value for each of the local subscription records?
Update
Using Adam's example below I get a 404 response from GoCardless. I think it's due to me not setting the merchant ID in the request. When I change the method to:
def gc_subscription
#gc_subscription ||= GoCardless::Merchant.find("MERCHANTID").subscriptions.find(self.resource_id)
end
I get undefined methodinterval' for #` for any attribute I try and request using the following code:
<% for subscription in #subscriptions %>
<%= subscription.gc_subscription.amount
<% end %>
When using the same code to get local content it works as expected:
<% for subscription in #subscriptions %>
<%= subscription.resource_id %>
<% end %>
I've checked that the value I am trying to retrieve is available in the API. https://sandbox.gocardless.com/docs/api_guide#resources-available
Update Two
As before calling the first result works using Adam's method:
<%= subscription.gc_subscription.first.amount %>
This returns 2.5 which is the value of the first subscription.

Answer 1

If I had a local Subscription model which linked to a remote data source I would have a method like this on my Subscription model which provided access to the remote object:
def gc_subscription
#gc_subscription ||= GoCardless::Subscription.find(self.resource_id)
end
Then you can access this method as necessary without any need for any GC logic in the view or controller. For example:
for subscription in #subscriptions
subscription.gc_subscription.some_method #=> "output"
end
Or, if you are only working with one subscription:
subscription = Subscription.find(id)
subscription #=> Your local Subscription instance
subscription.gc_subscription #=> GoCardless::Subscription instance
With it configured like that, you will be able to remove the #gocardless from your controller and replace your view with this:
<% #subscriptions.each do |subscription| %>
<tr>
<td><%= subscription.resource_id %></td>
<td><%= subscription.resource_type %></td>
<td><%= subscription.signature %></td>
<td><%= subscription.state %></td>
<td><%= subscription.gc_subscription.next_interval_start %></td>
<td><%= link_to 'Show', subscription %></td>
<td><%= link_to 'Edit', edit_subscription_path(subscription) %></td>
<td><%= link_to 'Destroy', subscription, method: :delete, data: { confirm: 'Are you sure?' } %></td>
</tr>
<% end %>
I hope that helps.