When and how to use ActiveRecord::Migration

Interestingly, the text book

Practical Ruby Gems
http://www.apress.com/book/view/9781590598115
listing 5-1

uses ActiveRecord::Base wheras ActiveRecord::Migration would give more
flexibility, right?

How would I implement this change, pls?

[email protected]:~/projects/aggregator$
[email protected]:~/projects/aggregator$ cat rss2mysql.rb
require ‘rubygems’
require ‘active_record’
require ‘feed_tools’
require ‘yaml’
require ‘items’

def all

feed_url = ‘http://www.slashdot.org/index.rss

feed=FeedTools::Feed.open(feed_url)
feed.items.each do |feed_item|
unless (Items.find_by_title(feed_item.title)
or Items.find_by_url(feed_item.link)
or Items.find_by_guid(feed_item.guid))
puts “processing item ‘#{feed_item.title}’ - new”

Items.new do |newitem|
   newitem.title=feed_item.title.gsub(/<[^>]*>/, '')
   newitem.guid=feed_item.guid
   if feed_item.publisher.name
       newitem.source=feed_item.publisher.name
   end
   newitem.url=feed_item.link
   newitem.content=feed_item.description
   newitem.timestamp=feed_item.published
   newitem.save
end

else
puts “processing item ‘#{feed_item.title}’ - old”
end
end

end

Items.connect
all
[email protected]:~/projects/aggregator$
[email protected]:~/projects/aggregator$ cat items.rb

class Items < ActiveRecord::Base

def Items.connect

  db = YAML.load_file("database.yml")
ActiveRecord::Base.establish_connection(
    :adapter  => db["adapter"],
    :host   => db["host"],
    :username => db["username"],
    :password => db["password"],
    :database => db["database"])

If the table doesn’t exist, we’ll create it.

unless Items.table_exists?
ActiveRecord::Schema.define do
create_table :items do |t|
t.column :title, :string
t.column :content, :string
t.column :source, :string
t.column :url, :string
t.column :timestamp, :timestamp
t.column :keyword_id, :integer
t.column :guid, :string
t.column :html, :string
end
end
end

end #connect

end
[email protected]:~/projects/aggregator$
[email protected]:~/projects/aggregator$ cat items2.rb
class Items2 < ActiveRecord::Migration
def self.up
create_table :items do |t|
t.column :title, :string
t.column :content, :string
t.column :source, :string
t.column :url, :string
t.column :timestamp, :timestamp
t.column :keyword_id, :integer
t.column :guid, :string
t.column :html, :string
end
end
def self.down
drop_table :items
end
end
[email protected]:~/projects/aggregator$
[email protected]:~/projects/aggregator$

thanks,

Thufir

On Sep 23, 4:38 am, Thufir [email protected] wrote:

Interestingly, the text book

Practical Ruby Gemshttp://www.apress.com/book/view/9781590598115
listing 5-1

uses ActiveRecord::Base wheras ActiveRecord::Migration would give more
flexibility, right?

I imagine they are just showing you that there is more than one way to
do things.

How would I implement this change, pls?

Which change ?

Fred

On Sep 23, 12:30 am, Frederick C. [email protected]
wrote:

I imagine they are just showing you that there is more than one way to
do things.

How would I implement this change, pls?

Which change ?

What I mean is, if it’s

class Items < ActiveRecord::Migration

then there cannot be a query as below:

claims = Items.find( :all)

Or, I suppose you don’t query in that fashion, as the migration file
will basically just have self.up and down (for me). How is the
migration in AR linked to the Base class, which is queriable, in a non-
rails scenario?

I suppose the driver will invoke the migration, but how is the
migration tied to the model (the Item class, versus Items the
migration)?

thanks,

Thufir

On Oct 13, 6:15 am, Thufir [email protected] wrote:

On Sep 23, 12:30 am, Frederick C. [email protected]
wrote:

Which change ?

What I mean is, if it’s

class Items < ActiveRecord::Migration

then there cannot be a query as below:

claims = Items.find( :all)

Correct.

Or, I suppose you don’t query in that fashion, as the migration file
will basically just have self.up and down (for me). How is the
migration in AR linked to the Base class, which is queriable, in a non-
rails scenario?

I don’t think it is.

I suppose the driver will invoke the migration, but how is the
migration tied to the model (the Item class, versus Items the
migration)?

There is no correspondence between models and migrations. For a given
model there will frequently be a migration that creates the
appropriate table but you don’t have to go that way.

Fred

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