Using Allocate to Create ActiveRecord Objects

create.rb

j = Job.allocate
j.init_with('attributes' => {'name' => 'Awesome Shop', 'title' => 'Test Job', 'status' => 'complete'})
j.title  # => 'Test Job'

example.rb

class Shop < ActiveRecord::Base
  has_many :jobs
end

class Job < ActiveRecord::Base
  belongs_to :shop
end

# Example query
Job.find_by_sql('SELECT shops.name, jobs.title, jobs.status FROM shops, jobs WHERE shops.id = jobs.shop_id')

find_by_sql.rb

def find_by_sql(sql)
  connection.select_all(sanitize_sql(sql), "#{name} Load").collect! { |record| instantiate(record) }
end

init.rb

def instantiate(record)
  model = find_sti_class(record[inheritance_column]).allocate
  model.init_with('attributes' => record)
  model
end

runit.rb

x = Job.allocate
x.instance_variable_set(:@attributes, {'name' => 'Awesome Shop', 'title' => 'Test Job', 'status' => 'complete'})
x.instance_variable_set(:@attributes_cache, {})
x.instance_variable_set(:@new_record, false)
x.instance_variable_set(:@readonly, false)
x.instance_variable_set(:@destroyed, false)
x.instance_variable_set(:@marked_for_destruction, false)
x.instance_variable_set(:@previously_changed, {})
x.instance_variable_set(:@changed_attributes, {})
x.send(:_run_find_callbacks)
x.send(:_run_initialize_callbacks)

x.title   # => 'Test Job'