On Wednesday, 4 December 2013 19:00:31 UTC-5, Ruby-Forum.com User wrote:
>
> Solved (though I'm not entirely sure why this works):
>
> UtilityDatum.
> select("sum(ami_residential)").
> where(:utility => u).
> group("utility_id").
> reorder('').
> first
>
> The reorder() prevents the ORDER BY clause from being emitted, so the
> generated SQL is valid.
>
> --
> Posted via http://www.ruby-forum.com/.
>
The 'ORDER BY' and 'LIMIT' clauses are actually coming from the `first`
call on the end of the chain.
For what it's worth, if the first query you mentioned is the one you want
you may want to check out `ActiveRecord::Calculations`, in particular `sum`:
http://api.rubyonrails.org/classes/ActiveRecord/Calculations.html#method-i-sum
Your code would look like:
r = u.utility_data.group(:utility_id).sum(:ami_residential)
At this point, `r` is a Hash:
{ 42 => 127.25, 76 => 321.02, etc }
of utility_id => sum pairs.
If you just want data rolled up for *one* Utility (I'm guessing that's what
`u` in the code above is...) you could skip the group:
sum = u.utility_data.sum(:ami_residential)
This returns a single number, the sum for all the related records.
--Matt Jones
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