Question

I have a Rails 2.3.11 app which has two key Models:

• Activity
  • Transaction

Live site: http://iatidata.heroku.com
Github: https://github.com/markbrough/IATI-Data

Every transaction nests under an activity. Each activity has multiple transactions.

I think I’ve got confused about how associations work in Rails, but maybe what I’m trying to do isn’t possible.

Essentially, I want to get the total value of the transactions of all the activities which belong to each country. So how much money went to India, how much to Afghanistan, etc.

This works:

@thiscountry_activities.each do |a|
    @thiscountry_value = @thiscountry_value + a.transactions.sum(:value)
end

But this doesn’t work:

@thiscountry_value = @thiscountry_activities.transactions.sum(:value)

It gives this error:

undefined method `transactions' for #<Array:0xb5670038>

@thiscountry_activities is defined like this:

@activities = Activity.find(:all, :conditions=> @conditions)

This is placed within a loop which gets each recipient country code. @conditions are :

@conditions[:recipient_country_code]=*each recipient country code, e.g. AF*

Looks like I have some sort of association problem. This is how the models are set up:

class Transaction < ActiveRecord::Base
    belongs_to :activity
end

class Activity < ActiveRecord::Base
    has_and_belongs_to_many :policy_markers
    has_and_belongs_to_many :sectors
    has_many :transactions
end

I think this is probably quite a simple problem, but I can’t work out what’s going on. The two models are connected together via id (in Activity) and activity_id (in Transactions).

Thank you!

Answer 1

Nothing is broken, the find method in Rails2 returns an Array – and there is no transactions method on the Array class. Use the first thing you have that’s working, with the each iterator, or work from the other side – from Transaction and grouping by the activity. It’s been a while since I wrote Rails2 code, but it’ll be something like this:

Transaction.all( :select => "activity_id, SUM(value) AS total", :group => 'activity_id' )

That’s not ready to copy-paste into your app as-is because there are some things about your app which aren’t clear to me, but hopefully it sets you in the right direction.