Test case for Rails/Active Record bug 13044 (https://github.com/rails/rails/issues/13044) Note that this only reproduces using the "postgresql" database adapter. Prerequisites: local instance of PostgreSQL with database name "bug", user name "bug" and password "bug".

active_record_test.rb

unless File.exist?('Gemfile')
  File.write('Gemfile', <<-GEMFILE)
    source 'https://rubygems.org'
    gem 'rails', '=3.2.14'
    gem 'pg'
  GEMFILE

  system 'bundle'
end

require 'bundler'
Bundler.setup(:default)

require 'active_record'
require 'minitest/autorun'
require 'logger'

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(
  :adapter => 'postgresql',
  :host => 'localhost',
  :database => 'bug',
  :username => 'bug',
  :password => 'bug'
)
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  drop_table :clients
  drop_table :sessions
  drop_table :client_session_assignments

  create_table :clients do |t|
    t.string :name
  end

  create_table :sessions do |t|
    t.string :name
  end

  create_table :client_session_assignments do |t|
    t.belongs_to :client
    t.belongs_to :session
    t.decimal :score
  end
end

class Client < ActiveRecord::Base
  has_many :client_session_assignments
  has_many :sessions,
    :through => :client_session_assignments,
    :select => 'sessions.*, client_session_assignments.score'
end

class Session < ActiveRecord::Base
  has_many :client_session_assignments
  has_many :clients,
    :through => :client_session_assignments,
    :select => 'clients.*, client_session_assignments.score'
end

class ClientSessionAssignment < ActiveRecord::Base
  belongs_to :client
  belongs_to :session
end

class BugTest < ActiveSupport::TestCase
  def test_association_stuff
    client = Client.create!(:name => 'the-client')
    session = Session.create!(:name => 'the-session')
    assignment = ClientSessionAssignment.create!(:client => client, :session => session, :score => 123.4)

    assert_equal BigDecimal, assignment.score.class

    retrieved_client = Client.find(client.id)

    # BUG: This assert fails since the PostgreSQL database
    # adapter returns 'String' instead of the expected 'BigDecimal'.
    assert_equal BigDecimal, retrieved_client.sessions.first.score.class
  end
end