Question

I have the following .erb view in a Sinatra app:

<% sessions.each do |session| %>
    <%= session.balance_beginning %>
    <%= session.balance_ending %>
<% end %>

It works as expected, displaying the beginning and ending balances recorded for each session. I would like to calculate the net balances from within the .erb file, but I can’t figure out how to do it. I have tried variations of this:

<% sessions.each do |session| %>
    <%= session.balance_ending - session.balance_beginning %>
<% end %>

That doesn’t work. I receive the following error in Sinatra:

undefined method `-' for nil:NilClass

How do I do what I’m trying to do?

Answer 1

Right @Zabba, in this case I think you would add a method to your Session model so you could call session.net_balance.

Then in your balance_ending and balance_beginning methods you would want to handle nil, either raise an error or return zero if that is valid.