Question

Say I have this:

class Account
  ...
  property :charge, Decimal, :precision => 7, :scale => 2
  ...
  classy stuff
  ...

  def self.balance(prefix)
    x = Account.get(prefix.to_sym).order(:fields => [:charge]).sum(:charge)
    sprintf("%5.2f", x)
  end
end

(Edit: The value of all :charge fields is 0.13E2 (0.1E2 + 0.3E1). This is correctly returned. Only in a View does it seem to get borked from sprintf)

In IRB Account.balance(:AAA) returns => "13.00"

if I call Account.balance(:AAA) from a view I get TypeError at /accounts
can’t convert nil into Float

Account.balance(:AAA) works anywhere I call it except in a view. If I remove sprintf("%5.2f", x) I get 0.13E2 in my view. (using Account.balance(:AAA).to_f in a view gives me 13.0)

Is sinatra incompatible with sprintf? or am I not understanding how to use sprintf?

(Edit: This is the offending view:)

<section>
  <% @accounts.each do |account| %>
    <article>
      <h2><%= account.prefix %></h2>
      <span><p>This account belongs to <%= account.name %> & has a balance of $<%= Account.balance(account.prefix) %>.</p></span>
    </article>
  <% end %>
</section> 

Answer 1

Wouldn’t it make more sense to define balance as an instance method rather than a class method? It looks from your example like you’re calling balance in an account-specific way anyway, so why not make it:

# the model

class Account
  #...

  def balance
    amount = self.order(:fields => [:charge]).sum(:charge)
    sprintf "%5.2f", amount

    # or the infix version:
    "%5.2f" % amount
  end
end

,

# the view

...balance of $<%= account.balance %>...

I know that this doesn’t address sprintf per se, but the problem is more likely to be coming from the slightly convoluted lookup than from a built-in method. Even if my specific code doesn’t suit your application, it might be worth simplifying the lookup step, even if that involves a few more lines of code.

The advantage of this approach is that there is no doubt that you’ll be getting the right Account record.