Basically what I'm trying to do is get the sum of 2 columns and save those results in another. I guess I'm looking to do something like this: a = Product.find(:all) b = Product.sum("test + test2", :group => "id") a.test3 = b a.save Obviously that doesn't work, but I'm trying to achieve something like that. Any suggestions?
on 2009-01-16 14:07
on 2009-01-16 14:20
On 16 Jan 2009, at 10:19, Herman wrote: > that. Any suggestions? > Product.update "test3 = test+test2" would probably do it. Fred
on 2009-01-16 18:35
That didn't work. I received: ArgumentError: wrong number of arguments (1 for 2) I tried something like this and it also didn't work: Product.update_all("test3", :sum => "test"+"test2", :group => "id") I'd imagine I'm not that far off, but I can't figure it out. On Jan 16, 6:19 am, Frederick C. <email@example.com>
on 2009-01-16 20:42
On 16 Jan 2009, at 16:34, Herman wrote: > > That didn't work. I received: ArgumentError: wrong number of arguments > (1 for 2) > > I tried something like this and it also didn't work: > Product.update_all("test3", :sum => "test"+"test2", :group => "id") > oops, typo, should be Product.update_all "test3 = test+test2"
on 2009-01-16 22:31
Works great. Thank you so much! On Jan 16, 12:41 pm, Frederick C. <firstname.lastname@example.org>
on 2009-01-17 22:37
Just to give another perspective... Do you really need to save the sum? Could it be calculated whenever you need it? If you save the sum you need to be confident that nothing will cause your data to get out of sync, such as some update to 'test' that does not update the sum. If you decide you do want to save the sum, could the database management system handle it for you? E.g. in PostgreSQL you can define triggers - in this case a trigger could update the sum for you no matter how 'test' and 'test2' are updated. You'd then have much greater faith in the reliability of each sum.