Creating a new object with multiple associations

rubyonrails-talk
1

This is a pretty simple question but I haven't heard an answer for it yet.

Let's say that a Bid object belongs_to both an Auction and a User at the same time. To create a new object I could do something like user.bids.build which would associate the new bid with that user, or auction.bids.build which would associate the new Bid with the Auction, but I have no idea how to create a new bid that would be associate with both at the same time. I can of course force-feed the new bid object with the id of the Auction or User objects, but that is the stupid way to do it.

This is probably a very newb question, but it never came up with me before, and I don't remember reading about it anywhere.

2

Eleo wrote:

Let's say that a Bid object belongs_to both an Auction and a User at the same time. To create a new object I could do something like user.bids.build which would associate the new bid with that user, or auction.bids.build which would associate the new Bid with the Auction, but I have no idea how to create a new bid that would be associate with both at the same time. I can of course force-feed the new bid object with the id of the Auction or User objects, but that is the stupid way to do it.

Rather than explictly setting the Bid object's foreign key, either add the Bid object to the collection or assign the associated object:

@auction.bids << @user.bids.build(params[:bid])

or

@bid = @user.bids.build(params[:bid]) @bid.auction = @auction @bid.save!

3

Hmm I guess that will work. I like the first example because it uses less lines.

4

I'd personally prefer something more semantically meaningful, thus delegating the creation and association of a bid to the model domain:

class User < ...

  def bids_on(auction, bid_params)     bid = Bid.new(bid_params)     bid.auction = auction     bid.user = self     bid.save!   end

end

And then in your controller:

@user.bids_on(auction, params[:bid])

This makes it immediately obvious what's going on, and the implementation details are neatly encapsulated in the model.

Cheers, Max