Problem with using joins with Arel tables and Rails queries

Arel joins problem

Because of the way I've structure the requests model and it's relationship with ads, I need to be able to do ORs in my query.

Anyway I've found my way to Arel and it looks like it should do the goods for me but I can't get a join working

The existing named scope in the Request class is

	scope :responder, lambda { |user| joins(:ad).where(:ads => { :user_id => user }) } 

The above works as I expect it to.

According to the doco I can find I should be able to do something like the following to get it working with Arel

	  requests = Request.arel_table
	  ads = Ad.arel_table
	  where(requests.join(ads).on(ads[:id].eq(requests[:ad_id])))

This results in an error

	TypeError: Cannot visit Arel::SelectManager

I can do the following in the console though

	r = Request.arel_table
	a = Ad.arel_table

	r.join(a).to_sql
	 => "SELECT  FROM \"requests\" INNER JOIN \"ads\" " 

So it looks like it's forming the SQL request, however when you put that in a where

	Request.where(r.join(a)).to_sql

I get the following

	TypeError: Cannot visit Arel::SelectManager....

I've tried doing other Arel actions within the where and it works (e.g.)

	Request.where(r[:status].eq(nil)).to_sql
	 => "SELECT \"requests\".* FROM \"requests\" WHERE (\"requests\".\"status\" IS NULL)"

Any ideas?

I'm encountering the same issue. Have you found a solution?

I can't remember exactly what I was doing :). I believe I actually changed my approach as this was quite an expensive database interaction. I also posted this to stackoverflow which netted some interesting comments. When I get a chance I'll take a look and see if I can find out what I eventually did.

http://stackoverflow.com/questions/5072709/arel-joins-and-rails-queries