From: Adam Boyle <briefcase.speakers@...>
Date: 2007-10-31T23:30:13+09:00
Subject: Extending ActiveRecord for csv export... a better way?

I accidentally posted this to the RoR forum; my apologies to anyone who
receives this twice.

As a new Ruby user (JRuby, actually), I've picked up this language with
a very specific purpose: to export data from a JDBC database into flat
files.  I've figured out how to get the data out of the DB and into a
file (using ActiveRecord-JDBC), but it requires a bit too much
configuration.  My first stab implementation requires me to define an
activerecord class for each table I want to export, and to define a
method all_columns in each class
that lays out the columns in the correct order.  I've also setup a
module (CSVable) that extends ActiveRecord so I can call the export
function directly on each class.  Here is the code:
-----------------------------------------
# Module definition
module CSVable
  extend ActiveRecord
  class Base < ActiveRecord::Base
    def self.export_table_to_csv(delimiter = ",", options = nil)
      File.open("#{self.table_name}.dat",
File::WRONLY|File::TRUNC|File::CREAT) do |file|
        self.find(:all, options).each do |trow|
          file.puts trow.all_columns.join(delimiter)
        end
      end
    end
  end
end

# Class definitions
class USR_USER_ACCOUNT < CSVable::Base
  set_table_name "USR.USER_ACCOUNT"
  def all_columns
    [ self.UID, self.USER_NAME, self.USER_INIT, self.ACTIVE_FLAG,
self.LAST_MODFD_TS ]
  end
end

class GRP_GRP < CSVable::Base
  set_table_name "GRP.GRP"
  def all_columns
    [ self.PARTY_ROLE_ASSIGN_PID, self.GRP_NBR_ID,
self.LAST_MODIFIED_TIMESTAMP ]
  end
end
...

# Usage for the module
USR_USER_ACCOUNT.export_table_to_csv("|")
-----------------------------------------

The major problem with this approach is that I have to setup all the
column info for each of the 36 tables.  Is there an easier way to get an
array of the columns while still retaining the original order?

I've tried using the attributes method, but since it returns a hash, the
columns are not in order.  My dabbles with the columns method have not
been successful either. Any ideas?

I also have a feeling there is a much better way to implement the export
function...

Any help or suggestions are most appreciated!

-Adam
-- 
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