Model.send append - ruby-on-rails

Question

I'm using:
ranking = Ranking.create()
ranking.send("#{month}=", rank)
ranking.save!
I'd like to append whatever value is in the #{month} column, not replace it. For example, if I am performing:
month = 'january'
ranking.send("#{month}=", 500)
ranking.save!
And then again later on:
month = 'january'
ranking.send("#{month}=", 250)
ranking.save!
The value for the column january for that particular ranking should be 750.
Is this possible with the current ActiveRecord API?

Answer 1

You could do this with increment! method
month = 'january'
ranking.increment!(month, 250)
updated:
to proof comments question (e.g. month = 'jan'):
irb(main):011:0> p.increment!(month, 70)
(0.0ms) begin transaction
SQL (0.0ms) UPDATE "products" SET "jan" = ?, "updated_at" = ? WHERE "product
"."id" = 1 [["jan", 171], ["updated_at", Sun, 06 Oct 2013 04:23:54 UTC +00:00]
(0.0ms) commit transaction
=> true
irb(main):012:0> p
=> #<Product id: 1, name: nil, description: nil, jan: 171, created_at: "2013-10-
06 04:22:50", updated_at: "2013-10-06 04:23:54">
and another case
irb(main):013:0> p.increment!("#{month}", 70)
(0.0ms) begin transaction
SQL (0.0ms) UPDATE "products" SET "jan" = ?, "updated_at" = ? WHERE "products
"."id" = 1 [["jan", 241], ["updated_at", Sun, 06 Oct 2013 04:24:10 UTC +00:00]]
(0.0ms) commit transaction
=> true
irb(main):014:0> p
=> #<Product id: 1, name: nil, description: nil, jan: 241, created_at: "2013-10-
06 04:22:50", updated_at: "2013-10-06 04:24:10">