rails sum multiple fields

I'm trying to do this supposingly simple operation in rails:

self.timesheets.select("sum(total) as total, sum(quantity) as quantity").first where self is a project

When I do it in console mode, it works but it renders me 3 columns:

[#<Timesheet id: nil, quantity: 120.1, total: 6245.2>]

When I run it in the app, I get this error message:

PG::GroupingError - ERROR:  column "timesheets.id" must appear in the GROUP BY clause or be used in an aggregate function
LINE 1: ..."  WHERE "timesheets"."project_id" = $1  ORDER BY "timesheet...
                                                             ^
:
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  activerecord-deprecated_finders (1.0.3) lib/active_record/deprecated_finders/relation.rb:129:in `first'
  app/models/project.rb:27:in `recalc_spendings'
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  -e:1:in `<main>'

I'm not really surprised by this message as the id is added to the query'result.

But why is it added by activerecord and how can I solve this?

Thanks!

EDIT

Thanks to PriteshJ, I understood that the ID was included by the "first" statement added at the end of my query to tell activerecord that it is a single record, not a collection.

So I know that I must get rid of first clause but when I do this, I get another error message:

NoMethodError: undefined method `total' for #<ActiveRecord::Relation::ActiveRecord_Relation_Timesheet:0x007fe73da50470>
from /usr/local/rvm/gems/ruby-2.0.0-p0/gems/activerecord-4.0.0/lib/active_record/relation/delegation.rb:121:in `method_missing'

This is normal because it is looking into a relation instead of a single record but I don't know how to solve it.

Should be simple though...

回答1:

It looks like you are ordering the results by timesheets.id or you have some default order scope or somewhere you are adding a order.

Remove the ordering or add the column to select by which you are ordering the query.

UPDATE:

try using

self.timesheets.select("sum(total) as total, sum(quantity) as quantity").to_a.first

.first in activerecord will try to sort the query and pick first element so first by using .to_a take the result first then do .first

回答2:

I think select is not the method you want to be using since you're not actually selecting a row in the db.

Perhaps sum is what you want (If I understand the problem correctly).

Would this work for you?:

total = project.timesheets.sum(:total)
quantity = project.timesheets.sum(:quantity)

回答3:

With squeel gem, it is easy.

self.timesheets.select{[sum(:total).as(:total), sum(:quantity).as(:quantity)]}

回答4:

self.timesheets.pluck("sum(total)", "sum(quantity)")

回答5:

If you use select it will attempt to build a model with the fields you specified. You would be better of using pluck as suggested by jackpipe. However, I would make one alteration - methods like sum will return 0 if there are no records, but pluck will return nil, so to overcome that you could try this:

total, quantity = self.timesheets.pluck("sum(total)", "sum(quantity)").first.map(&:to_i)