I have a db Orders with fields qty and amount, and another linked db
Person that has many Orders. I''ve been using this to sum all of the
products of qty and amount:
Person.find( person ).orders.inject( 0 ){ |sum, order| sum +
( order.qty * order.amount ) }
Is there another/better way to do this in ActiveRecord?
Many TIA,
Craig
Dudebot wrote:> I have a db Orders with fields qty and amount, and another linked db > Person that has many Orders. I''ve been using this to sum all of the > products of qty and amount: > > Person.find( person ).orders.inject( 0 ){ |sum, order| sum + > ( order.qty * order.amount ) } > > Is there another/better way to do this in ActiveRecord?Yes: use the DB''s sum() function. ActiveRecord::Calculations could help you with this if you were summing a single field, but since you''re summing a complex expression, you may have to use raw SQL.> > Many TIA, > CraigBest, -- Marnen Laibow-Koser http://www.marnen.org marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org -- Posted via http://www.ruby-forum.com/.
Thanks--I tried a bunch of different incarnations using sum() without luck, and as I was starting to write raw SQL, I decided it would be easier to read/more maintainable code just to use Ruby. The db is small, and performance degradation should not be an issue. On Sep 28, 8:23 am, Marnen Laibow-Koser <rails-mailing-l...@andreas- s.net> wrote:> Dudebot wrote: > > I have a db Orders with fields qty and amount, and another linked db > > Person that has many Orders. I''ve been using this to sum all of the > > products of qty and amount: > > > Person.find( person ).orders.inject( 0 ){ |sum, order| sum + > > ( order.qty * order.amount ) } > > > Is there another/better way to do this in ActiveRecord? > > Yes: use the DB''s sum() function. ActiveRecord::Calculations could help > you with this if you were summing a single field, but since you''re > summing a complex expression, you may have to use raw SQL. > > > > > Many TIA, > > Craig > > Best, > -- > Marnen Laibow-Koserhttp://www.marnen.org > mar...-sbuyVjPbboAdnm+yROfE0A@public.gmane.org > -- > Posted viahttp://www.ruby-forum.com/.
Dudebot wrote:> Thanks--I tried a bunch of different incarnations using sum() without > luck, and as I was starting to write raw SQL, I decided it would be > easier to read/more maintainable code just to use Ruby.You got it backwards. In this case, doing the calculation on the DB side will be more maintainable.> The db is > small, and performance degradation should not be an issue.I wonder. What you''re doing now sends lots of unnecessary data from the DB to the app. Doing it on the DB side will avoid this problem. I don''t see a single good reason for doing the calculation in Ruby in this case.> > On Sep 28, 8:23�am, Marnen Laibow-Koser <rails-mailing-l...@andreas-Best, -- Marnen Laibow-Koser http://www.marnen.org marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org -- Posted via http://www.ruby-forum.com/.