RoR投票系统在本地工作，但在Heroku上部署时则不行

Question

My app implements 'ideas' that users can vote on and 'unvote'. It works fine locally. When pushed to Heroku, users can vote but the 'unvote' action does not work and generates a "We're sorry, but something went wrong." page from herokuapp.com.

I've checked the heroku logs and the error is as follows :

2012-05-25T09:47:18+00:00 app[web.1]: Started POST "/ideas/remove_vote/1/1" for 88.171.195.199 at 2012-05-25 09:47:18 +0000
2012-05-25T09:47:18+00:00 app[web.1]: Processing by IdeasController#remove_vote as HTML
2012-05-25T09:47:18+00:00 app[web.1]:   Parameters: {"authenticity_token"=>"mJ5daJfBhf+823VTg9C1+YSBdqVFTFPuJWiO2cIx6iQ=", "u_id"=>"1", "i_id"=>"1"}
2012-05-25T09:47:18+00:00 app[web.1]: Completed 500 Internal Server Error in 8ms
2012-05-25T09:47:18+00:00 app[web.1]: : DELETE FROM "votes" WHERE "votes"."" = $1):
2012-05-25T09:47:18+00:00 app[web.1]:   app/controllers/ideas_controller.rb:85:in `remove_vote'
2012-05-25T09:47:18+00:00 app[web.1]: 
2012-05-25T09:47:18+00:00 app[web.1]: ActiveRecord::StatementInvalid (PG::Error: ERROR:  zero-length delimited identifier at or near """"
2012-05-25T09:47:18+00:00 app[web.1]:                                           ^
2012-05-25T09:47:18+00:00 app[web.1]: LINE 1: DELETE FROM "votes" WHERE "votes"."" = $1
2012-05-25T09:47:18+00:00 app[web.1]: 
2012-05-25T09:47:18+00:00 app[web.1]: cache: [POST /ideas/remove_vote/1/1] invalidate, pass
2012-05-25T09:47:18+00:00 app[web.1]: 

My remove_vote method in ideas_controller.rb is the following :

def remove_vote
  @vote = Vote.find_by_user_id_and_idea_id(params[:u_id], params[:i_id])
  @vote.destroy
  redirect_to ideas_path
end

Would any of you have an idea to fix this? I suspect it has something to do with the fact that the local database is SQLite and the production one on Heroku is PostgreSQL but I find it strange that adding a vote works and that removing one does not.

Answer 1

Take a look at the delete statement being issued in that log: DELETE FROM "votes" WHERE "votes"."" = $1

What column is that where clause talking about? What column should it be talking about? Is there anything in the Vote model that explains it not using the id column?

Answer 2

When you run into issues like this it is a good idea to configure/run your application locally using postgres. This will allow you to debug these issues locally rather than trying to 'guess' what the problem is on Heroku.

Here is a good railscast on getting postgres running locally.

http://railscasts.com/episodes/342-migrating-to-postgresql