Trying to use multiple databases - getting ActiveRecord Connection Not Established

Question

I'm trying to set up ActiveRecord so I can use multiple database connections in my application. I am not using Rails.

To do this, I set up an abstract class for each of my databases:

  class BuoyDatabase < ActiveRecord::Base
    self.abstract_class = true
    establish_connection $database_config['buoy_database']
  end

Then I inherit from the OneDatabase class:

  class Buoy < BuoyDatabase
    has_many :buoyDatas, :foreign_key => 'buoy_id'
  end

  class BuoyData < BuoyDatabase
    belongs_to :buoy
  end

I can successfully create and read instances of both Buoy and BuoyData, but I can't get any related records:

Buoy.find_by_id(...).buoyDatas  # gives ActiveRecord::ConnectionNotEstablished

Details of the error:

ActiveRecord::ConnectionNotEstablished: ActiveRecord::ConnectionNotEstablished
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/connection_adapters/abstract/connection_pool.rb:409:in `retrieve_connection'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/connection_adapters/abstract/connection_specification.rb:107:in `retrieve_connection'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/connection_adapters/abstract/connection_specification.rb:89:in `connection'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/alias_tracker.rb:69:in `connection'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/alias_tracker.rb:54:in `initial_count_for'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/alias_tracker.rb:12:in `block in initialize'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/alias_tracker.rb:29:in `yield'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/alias_tracker.rb:29:in `default'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/alias_tracker.rb:29:in `aliased_name_for'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/alias_tracker.rb:17:in `aliased_table_for'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/join_helper.rb:15:in `block in construct_tables'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/join_helper.rb:14:in `each'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/join_helper.rb:14:in `construct_tables'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/association_scope.rb:53:in `add_constraints'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/association_scope.rb:33:in `scope'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/association.rb:99:in `association_scope'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/association.rb:88:in `scoped'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/collection_association.rb:367:in `find_target'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/collection_association.rb:324:in `load_target'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/collection_proxy.rb:51:in `load_target'
from /Users/admin/.rvm/rubies/ruby-1.9.3-head/lib/ruby/gems/1.9.1/gems/activerecord-3.1.0/lib/active_record/associations/collection_proxy.rb:89:in `method_missing'

Answer 1

The workaround is to establish a connection on ActiveRecord::Base itself. It doesn't matter to which database the connection is made. This connection is only needed so that ActiveRecord can get the meta information necessary to handle associations and whatnot. You need not use the connection at all, once established.

This issue is a duplicate of ActiveRecord 3.1.0 multiple databases and the workaround is first described here: https://stackoverflow.com/a/7406374/29729