Advanced Rails - Building Industrial-Strength Web Apps in Record Time

Incorporating Rails Components | 285

ETL operations

ActiveRecord can be a useful tool to load data into and extract data from databases.
It can be used for anything from one-off migration scripts to hourly data transforma-
tion jobs. The following is a representative example, using James Edward Gray II’s
FasterCSV library:

require 'rubygems'

require 'fastercsv' # gem install fastercsv

require 'active_record'

# Set up AR connection and define User class

ActiveRecord::Base.establish_connection(

# (connection spec)...

)

class User

# The table we're importing into doesn't use Rails conventions,

# so we'll override some defaults.

set_table_name 'user'

set_primary_key 'userid'

end

FasterCSV.foreach('users.csv', :headers => true) do |row|

# The CSV header fields correspond to the database column names,

# so we can do this directly, with no mapping.

User.create! row.to_hash

end

Schema operations

ActiveRecord’s migration methods can be used as a portable abstraction for SQL
data definition language (DDL). TheActiveRecord::Schema.definefunction allows
you to use the ActiveRecord schema definition statements within a block to perform
operations on a database. The full set of DDL operations is documented in
ActiveRecord::ConnectionAdapters::SchemaStatements.

require 'rubygems'

require 'active_record'

ActiveRecord::Base.establish_connection(

# (connection spec)...

)

ActiveRecord::Schema.define do

create_table :sites do |t|

t.string :name, :null => false

t.string :city

t.string :state

end

add_column :users, :site_id, :integer

add_index :users, :site_id

end