I found migrations to be very useful tool to maintain data structures in a rails project. It is clean, easy to understand and fast when it comes to recreate a database.
During develoment, I faced several times the same problem: “How to import static data into the database?” Of course, one can create fixture and load it. But sometimes one needs more powerful tool.
So, I tried to import the data in the migrations themselves. Since the data to import was huge (tens of MBs), I did try several methods and approaches. Here is the result.
Fixtures in Migrations
This is method that I found on the web in an article of Adam Christensen Loading Fixtures in a Migration. It shows how to load the fixtures file into database.
require 'active_record/fixtures'
class CreateCategories < ActiveRecord::Migration
def self.up
create_table :categories do |t|
t.column :name, :string
end
Fixtures.create_fixtures(’test/fixtures’, File.basename(”categories.yml”, ‘.*’))
end
def self.down
drop_table :categories
end
end
Active record way
If your ActiveRecord object already exists, you can use the following code. It is obviously not the way to import thousands of records, but for ten objects it is good enough.
class CreateAuthors < ActiveRecord::Migration
def self.up
create_table :authors do |t|
t.column :name, :string, :length=>20, :null=>false
t.column :surname, :string, :length=>50, :null=>false
t.column :blog, :string, :length=>100, :default=>'http://blog.zmok.net'
end
Author.create( :name=>'Roman', :surname=>'Mackovcak')
end
def self.down
drop_table :authors
end
end
External CSV
If the data came in the CSV format then a fastercsv library could be used.
First of all, the library needs to be installed.
sudo gem install fastercsv
then create the migration
require 'fastercsv'
class LoadAuthors < ActiveRecord::Migration
def self.up
FasterCSV.foreach(’db/data/authors.csv’) do |row|
Author.create(:name=>row<sup><a href=”#fn14068651694926bca8a5dde”>0</a></sup>, :surname=>row<sup><a href=”#fn10810929634926bca8a6d82″>1</a></sup>, :blog=>row<sup><a href=”#fn1048664414926bca8a7d1a”>2</a></sup>)
end
end
def self.down
Author.delete_all
end
end
And place the CSV file (example below) into db/data folder.
"Miro","Skultety","http://blog.zmok.net"
"Abhishek","Balaria","http://blog.zmok.net"
Embedded CSV
Sometimes it is useful to bundle the data directly with the migration. In this example, the data are provided to the load_articles method from articles_data.
require 'csv'
class CreateArticles < ActiveRecord::Migration
def self.up
create_table :articles do |t|
t.column :title, :string, :length=>20, :null=>false
t.column :url, :string, :length=>100, :null=>false
t.column :author_id, :integer, :null=>false
t.column :abstract, :string, :length=>255
end
load_articles
end
def self.down
drop_table :articles
end
def self.load_articles
cnx = ActiveRecord::Base.connection
ActiveRecord::Base.silence do
reader = CSV::Reader.create(articles_data)
reader.each do |row|
values = row.collect {|v| cnx.quote(v).gsub(’\\n’, “\n”).gsub(’\\r’, “\r”) }.join(’, ‘)
sql = “INSERT INTO articles(id, title, url, author_id, abstract) VALUES (#{values})”
cnx.insert(sql)
end
end
end
def self.articles_data
<<’END_OF_DATA’
1,”Integration is the killer app (even in Web 2.0)”,”http://blog.zmok.net/articles/2006/08/20/integration-is-the-killer-app-even-in-web-2-0″,3,”Integration is the key to success”
2,”Visualize your Rails schema”,”http://blog.zmok.net/articles/2006/11/13/visualize-your-rails-schema”,2,”Exporting rails schema to UML”
END_OF_DATA
end
end
ActiveRecord – native commands
Last, but not least is the method that uses native functions of MySQL database. This could work only if the rails application sits on the same machine as the MySQL.
require 'tempfile'
class CreateReaders < ActiveRecord::Migration
def self.up
create_table :readers do |t|
t.column :nickname, :string, :length=>20, :null=>false
t.column :email, :string, :length=>50, :null=>false
end
load_from_file
end
def self.down
drop_table :readers
end
def self.load_from_file
file = ‘db/data/readers.csv’
tp = Tempfile.new(File.basename(file)).path
File.copy(file, tp)
File.chmod(0666, tp)
ActiveRecord::Base.connection.execute(”load data infile \’#{tp}\’ into table readers fields terminated by \’,\’ enclosed by \’\”\’ lines terminated by \’\\n\’”)
end
end
and the corresponding CSV file
1,"bob","bob@really-cool-office.org"
2,"sergey","sergey@hermitage-magazin.ru"
That’s it! Enjoy it.
