The problem is in the pk_and_sequence_for method in PostgreSQLAdapter - the query doesn't find anything for the stock_trades table. The query could probably adapted to work with table inheritance, however I'd caution against using it because you're likely to come up against other problems, especially when loading/dumping schemas, migrations, etc.

Hey Pixeltrix

Been playing around with this again and noticed that adding self.columns_hash['id'].primary = true to an ActiveRecord model fixes the issue I am having with the primary key. As such, my models look as follows:

# trade.rb
class Trade < ActiveRecord::Base
  self.abstract_class = true

  def expensive?
    self.price > 100
  end

  def alot?
    self.quantity > 100
  end
end

# stock_trade.rb
class StockTrade < Trade
  self.columns_hash['id'].primary = true
end

# bond_trade.rb
class BondTrade < Trade
  self.columns_hash['id'].primary = true
end

Do you see any problems with doing this, or if support for this will ever be rolled into Rails proper?

I've checked it on both master and 3-2-stable and it works correctly. @robertsosinski let me know if this is still an issue for you.

Just to add for posterity, I had this same issue when using "acts_as_nested_set" and MY fix was not to put in the self.columns_hash ['id'] line, but to do this in my parent class:

parent

#...
self.abstract_class = true

def self.inherited(base)
  base.acts_as_nested_set
end

#...

child

class ChildThing < ParentThing
end

worked fine for me!

Unfortunately, neither of these solutions worked for me on a Rails 3.2.17. For my needs I ended up sorting the array in memory after pulling from the DB.

pk_and_sequence_for doesn't exists in master so pixeltrix's link is no longer valid, but here's the 3.2-stable function.