gistfile1.rb

class Business
  many :invoices
end

class Invoice
  property :ref, String
  property :total, BigDecimal
  property :paid_total, BigDecimal

  one :buinsess
  
  
  index [:business, :ref] #key like "#{business_key}_invoices_#{ref}}"
  index [:business, :paid], :if => ->{|me| me.paid_total >= me.total} #key like "#{business_key}_invoices_paid"
  index [:business, :unpaid], :if => ->{|me| me.paid_total < me.total} #key like "#{business_key}_invoices_unpaid"
end


b = business.find(1)
b.invoices.count # 3
b.invoices.paid.count #2
b.invoices.unpaid.count #1