class Auction
belongs_to :item
belongs_to :user, :foreign_key => :current_winner_id
has_many :auction_bids
end
class User
has_many :auction_bids
end
class AuctionBid
belongs_to :auction
belongs_to :user
end
An auction is displayed on the page, the user enters an amount and clicks bid. Controller code might look something like this:
class MyController
def bid
@ab = AuctionBid.new(params[:auction_bid])
@ab.user = current_user
if @ab.save
render :json => {:response => 'YAY!'}
else
render :json => {:response => 'FAIL!'}
end
end
end
This works great so far! However, I need to ensure a couple other things happen.
@ab.auction.bid_count
needs to be incremented by one.@ab.user.bid_count
needs to be incremented by one@ab.auction.current_winner_id
needs to be set to @ab.user_id
That is, the User
and the Auction
associated with the AuctionBid
need values updated as well in order for the AuctionBid#save
to return true.
Both Base#save and Base#destroy come wrapped in a transaction that ensures that whatever you do in validations or callbacks will happen under the protected cover of a transaction. So you can use validations to check for values that the transaction depends on or you can raise exceptions in the callbacks to rollback, including after_* callbacks.
class AuctionBid < ActiveRecord::Base
belongs_to :auction, :counter_cache => true
belongs_to :user
validate :auction_bidable?
validate :user_can_bid?
validates_presence_of :auction_id
validates_presence_of :user_id
# the real magic!
after_save :update_auction, :update_user
def auction_bidable?
errors.add_to_base("You cannot bid on this auction!") unless auction.bidable?
end
def user_can_bid?
errors.add_to_base("You cannot bid on this auction!") unless user.can_bid?
end
protected
def update_auction
auction.place_bid(user)
auction.save!
end
def update_user
user.place_bid
user.save!
end
end
François Beausoleil +1. Thanks for the :foreign_key
recommendation, but the current_winner_*
columns need to be cached in the db in order to optimize the query.
Alex +1. Thanks for getting me started with Model.transaction { ... }
. While this didn't end up being a complete solution for me, it definitely help point me in the right direction.
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