test.rb

require "active_record"
require "logger"

puts ActiveRecord::VERSION::STRING

$rails4 = ActiveRecord::VERSION::MAJOR > 3

ActiveRecord::Base.establish_connection adapter: 'sqlite3', database: ':memory:'

ActiveRecord::Schema.define do
  create_table :people
  create_table :accesses
  create_table :projects
end

class Person < ActiveRecord::Base
  has_many :accesses

  if $rails4
    has_many :projects, -> { where foo: 'a' }, through: :accesses
  else
    has_many :projects, conditions: { foo: 'a' }, through: :accesses
  end
end

class Access < ActiveRecord::Base
  belongs_to :person

  if $rails4
    belongs_to :project, -> { where foo: 'b' }
  else
    belongs_to :project, conditions: { foo: 'b' }
  end
end

class Project < ActiveRecord::Base
  default_scope -> { where foo: 'c' }
end

person = Person.create
puts person.projects.to_sql