Is sprintf incompatible with sinatra? - ruby

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.

Answer 2

tested it with a little sinatra app and it worked for me
app.rb
#!/usr/bin/env ruby
require 'rubygems'
require 'sinatra'
get '/' do
#x = 10.23
erb :index
end
views/index.erb
<%= sprintf("%5.2f", #x) %>
output:
10.23
ruby 1.9.2 / sinatra 1.3.1
I think there is another error before the sprintf because of your error message:
can't convert nil into Float
seems like your x is nil. try to be sure that x is not nil there, then sprintf should work as expected.