> Could you please recommend elegant way (read - best practices in
> "Rails way", less DB calls) to solve the following situation ?
>
> I have 2 tables:
>
> Meter
> - has_many :meter_records
>
> MeterRecord
> - belong_to :meter
>
> I have to calculate difference between meter's current month record
> and same meter's previous month record.
>
> I would like to avoid unnecessary selects from DB and also avoid
> dealing with SQL - I prefer functionality provided by ActiveRecord.
>
> Can you please recommend the solution or at least point me to a good
> tutorial ?
>
> Thank you in advance.
No idea if this is best practice, but I'd put it in a method in the Meter model
and just do it...
class Meter...
def meth
c, l = meter_records.order('created_at desc').limit(2)
c.some_field - l.some_field
end
end
I'm making some assumptions about your models of course, but the above should
get you started.
-philip
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