dan.thoughts

Sometimes ORM just cant hand some complicated query, especially when the results of such query does not refer to any table.

For Rails ActiveRecord:

class Item < ActiveRecord::Base
   def self.some_heavy_stuff(param)
     sql = self.sanitize_sql(['.... SQL ....', param)
     self.connection.execute(sql)
   end
end
 
# usage
data = Item.some_heavy_stuff(1)
data.each do |row|
   puts row['id']
end

For DataMapper its almost the same (they`ve replaced query method with select not a long time ago):

class Item
  include DataMapper::Resource
 
  property :id, Serial
  property :foo, String
  property :bar, String
 
  def self.some_heavy_stuff(param)
     repository(:default).adapter.select('... SQL ...')
  end
end

Since i`ve been using both DataMapper (Merb/Sinatra) and ActiveRecord (Rails) a lot i noticed that AR acts weight when i manually set PK key, particularly ID field, which you dont have to define by default. In DM you have to define it as ‘Serial’.

So, the task is to create/update records in your database which is supposes to represent data from primary database. In such cases all ID`s should be unique and equal to each other.

To disable autoincremental ID field in your AR models just use this option:

create_table :foo, :id => false do |t|
  t.integer   :id, :options => 'PRIMARY KEY'
  # .... rest of columns
end