ActiveAdmin how to get sum from column

Question

I have a situation where I'd like to get the sum of one column and display it

e.g in activeadmin

ActiveAdmin.register Expense do    
   index do       

    column :amount 
    column :details
    column :created_at

    default_actions
  end         
end

I need to sum the amount column and show it. Also I can't figure out where to show the Total Sum, maybe the sidebar? If the results are filtered then the sum has to change accordingly to results shown.

Answer 1

You can avoid having to count up with a running total, by simply accessing the underlying collection which will take into account currently applied filters/scopes, and use reduce(:+) to perform the sum:

ActiveAdmin.register Expense do    
   index do       
    column :amount 
    column :details
    column :created_at

    default_actions

    div class: "panel" do
      h3 "Total amount: #{collection.pluck(:amount).reduce(:+)}"
    end
  end         
end