class QuestionSet < ActiveRecord::Base
  self.primary_keys = :question_set_id, :generation, :language_id
  has_many :question_set_questions,
      foreign_key: [:set_id, :set_generation],
      primary_key: [:question_set_id, :generation]
  has_many :questions, through: :question_set_questions
end

class QuestionSetQuestion < ActiveRecord::Base
  belongs_to :question_set,
      -> { where :language_id => Language.current_language.id },
      foreign_key: [:set_id, :set_generation],
      primary_key: [:question_set_id, :generation]
  belongs_to :question,
      -> { where :language_id => Language.current_language.id },
      foreign_key: [:question_id, :question_generation],
      primary_key: [:question_id, :generation]
end

class Question < ActiveRecord::Base
  self.primary_keys = :question_id, :generation, :language_id
  has_many :question_set_questions,
      foreign_key: [:question_id, :question_generation],
      primary_key: [:question_id, :generation]
  has_many :question_sets, through: :question_set_questions
end

qs = QuestionSet.first
qs.questions

q = Question.first
q.question_sets

qsq = QuestionSetQuestion.first
qsq.question
# or
qsq.question_set

Question.find([1,1,1])
# or
QuestionSet.find([1,1,1])

EXEC sp_executesql N'SELECT  [questions].* FROM [questions] WHERE ([questions].[question_id] = @0 AND [questions].[generat
ion] = @1 AND [questions].[language_id] = @2)  ORDER BY [questions].[question_id,generation,language_id] ASC OFFSET 0 ROWS FETCH NEXT 1 ROWS ONLY',
 N'@0 int, @1 int, @2 int', @0 = 1, @1 = 1, @2 = 1  [["question_id", 1], ["generation", 1], ["language_id", 1]]
TinyTds::Error: Invalid column name 'question_id,generation,language_id'.: EXEC sp_executesql N'SELECT  [questions].* FROM [questions] WHERE ([ques
tions].[question_id] = @0 AND [questions].[generation] = @1 AND [questions].[language_id] = @2)  ORDER BY [questions].[question_id,generation,langu
age_id] ASC OFFSET 0 ROWS FETCH NEXT 1 ROWS ONLY', N'@0 int, @1 int, @2 int', @0 = 1, @1 = 1, @2 = 1
ActiveRecord::StatementInvalid: TinyTds::Error: Invalid column name 'question_id,generation,language_id'.: EXEC sp_executesql N'SELECT  [questions]
.* FROM [questions] WHERE ([questions].[question_id] = @0 AND [questions].[generation] = @1 AND [questions].[language_id] = @2)  ORDER BY [question
s].[question_id,generation,language_id] ASC OFFSET 0 ROWS FETCH NEXT 1 ROWS ONLY', N'@0 int, @1 int, @2 int', @0 = 1, @1 = 1, @2 = 1
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-sqlserver-adapter-4.2.3/lib/active_record/connection_adapters/sqlser
ver/database_statements.rb:336:in `each'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-sqlserver-adapter-4.2.3/lib/active_record/connection_adapters/sqlser
ver/database_statements.rb:336:in `handle_to_names_and_values_dblib'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-sqlserver-adapter-4.2.3/lib/active_record/connection_adapters/sqlser
ver/database_statements.rb:325:in `handle_to_names_and_values'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-sqlserver-adapter-4.2.3/lib/active_record/connection_adapters/sqlser
ver/database_statements.rb:300:in `_raw_select'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-sqlserver-adapter-4.2.3/lib/active_record/connection_adapters/sqlser
ver/database_statements.rb:295:in `block in raw_select'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.2.0/lib/active_record/connection_adapters/abstract_adapter.rb:466:
in `block in log'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activesupport-4.2.0/lib/active_support/notifications/instrumenter.rb:20:in `instr
ument'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.2.0/lib/active_record/connection_adapters/abstract_adapter.rb:460:
in `log'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-sqlserver-adapter-4.2.3/lib/active_record/connection_adapters/sqlser
ver/database_statements.rb:295:in `raw_select'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-sqlserver-adapter-4.2.3/lib/active_record/connection_adapters/sqlser
ver/database_statements.rb:244:in `sp_executesql'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-sqlserver-adapter-4.2.3/lib/active_record/connection_adapters/sqlser
ver/database_statements.rb:19:in `exec_query'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-sqlserver-adapter-4.2.3/lib/active_record/connection_adapters/sqlser
ver/database_statements.rb:199:in `select'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.2.0/lib/active_record/connection_adapters/abstract/database_statem
ents.rb:32:in `select_all'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.2.0/lib/active_record/connection_adapters/abstract/query_cache.rb:
70:in `select_all'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.2.0/lib/active_record/querying.rb:39:in `find_by_sql'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.2.0/lib/active_record/relation.rb:638:in `exec_queries'
... 1 levels...
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.2.0/lib/active_record/relation.rb:243:in `to_a'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.2.0/lib/active_record/relation/finder_methods.rb:487:in `find_take
'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.2.0/lib/active_record/relation/finder_methods.rb:105:in `take'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/composite_primary_keys-8.1.0/lib/composite_primary_keys/relation/finder_methods.r
b:124:in `find_one'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/composite_primary_keys-8.1.0/lib/composite_primary_keys/relation/finder_methods.r
b:97:in `find_with_ids'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/activerecord-4.2.0/lib/active_record/relation/finder_methods.rb:71:in `find'
        from c:in `find'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/composite_primary_keys-8.1.0/lib/composite_primary_keys/core.rb:26:in `find'
        from (irb):1
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/railties-4.2.0/lib/rails/commands/console.rb:110:in `start'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/railties-4.2.0/lib/rails/commands/console.rb:9:in `start'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:68:in `console'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
        from c:/RailsInstaller/Ruby2.0.0/lib/ruby/gems/2.0.0/gems/railties-4.2.0/lib/rails/commands.rb:17:in `<top (required)>'
        from bin/rails:4:in `require'
        from bin/rails:4:in `<main>'irb(main):

TinyTds::Error: Invalid column name 'question_id,generation,language_id'