Seed Fu is an attempt to once and for all solve the problem of inserting and maintaining seed data in a database. It uses a variety of techniques gathered from various places around the web and combines them to create what is hopefully the most robust seed data system around.

Seed data is taken from the db/fixtures directory. Simply make descriptive .rb files in that directory (they can be named anything, but users.rb for the User model seed data makes sense, etc.). These scripts will be run whenever the db:seed (db:seed_fu for Rails 2.3.5 and greater) rake task is called, and in order (you can use 00_first.rb, 00_second.rb, etc). You can put arbitrary Ruby code in these files, but remember that it will be executed every time the rake task is called, so it needs to be runnable multiple times on the same database.

You can also have environment-specific seed data placed in db/fixtures/ENVIRONMENT that will only be loaded if that is the current environment.

Let’s say we want to populate a few default users. In db/fixtures/users.rb we write the following code:

User.seed(:login, :email) do |s|
  s.login = "bob"
  s.email = "bob@bobson.com"
  s.first_name = "Bob"
  s.last_name = "Bobson"
end

User.seed(:login, :email) do |s|
  s.login = "bob"
  s.email = "bob@stevenson.com"
  s.first_name = "Bob"
  s.last_name = "Stevenson"
end

That’s all you have to do! You will now have two users created in the system and you can change their first and last names in the users.rb file and it will be updated as such.

The arguments passed to the <ActiveRecord>.seed method are the constraining attributes: these must remain unchanged between db:seed calls to avoid data duplication. By default, seed data will constrain to the id like so:

Category.seed do |s|
  s.id = 1
  s.name = "Buttons"
end

Category.seed do |s|
  s.id = 2
  s.name = "Bobbins"
  s.parent_id = 1
end

Note that any constraints that are passed in must be present in the subsequent seed data setting.

The default .seed` syntax is very verbose. An alternative is the `.seed_many syntax. Look at this refactoring of the first seed usage example above:

User.seed_many(:login, :email, [
  { :login => "bob", :email => "bob@bobson.com",    :first_name => "Bob", :last_name = "Bobson" },
  { :login => "bob", :email => "bob@stevenson.com", :first_name => "Bob", :last_name = "Stevenson" }
])

Not as pretty, but much more concise.

Seed files can be huge. To handle large files (over a million rows), try these tricks:

• Gzip your fixtures. Seed Fu will read .rb.gz files happily. gzip -9 gives the best compression, and with Seed Fu’s repetitive syntax, a 160M file can shrink to 16M.

• Add lines reading # BREAK EVAL in your big fixtures, and Seed Fu will avoid loading the whole file into memory. If you use SeedFu::Writer, these breaks are built into your generated fixtures.

• Load a single fixture with the SEED environment variable: SEED=cities,states rake db:seed > seed_log`. Each argument to `SEED is used as a regex to filter fixtures by filename.

Say you have a CSV you need to massage and store as seed files. You can create an import script using SeedFu::Writer.

#!/usr/bin/env ruby
#
# This is: script/generate_cities_seed_from_csv
#
require 'rubygems'
require 'fastercsv'
require File.join( File.dirname(__FILE__), '..', 'vendor/plugins/seed-fu/lib/seed-fu/writer' )

# Maybe SEEF_FILE could be $stdout, hm.
#
CITY_CSV  = File.join( File.dirname(__FILE__), '..', 'city.csv' )
SEED_FILE = File.join( File.dirname(__FILE__), '..', 'db', 'fixtures', 'cities.rb' )

# Create a seed_writer, walk the CSV, add to the file.
#

seed_writer = SeedFu::Writer::SeedMany.new(
  :seed_file  => SEED_FILE,
  :seed_model => 'City',
  :seed_by    => [ :city, :state ]
)

FasterCSV.foreach( CITY_CSV,
  :return_headers => false,
  :headers => :first_row
) do |row|

  # Skip all but the US
  #
  next unless row['country_code'] == 'US'

  unless us_state
    puts "No State Match for #{row['region_name']}"
    next
  end

  # Write the seed
  #
  seed_writer.add_seed({
    :zip => row['zipcode'],
    :state => row['state'],
    :city => row['city'],
    :latitude => row['latitude'],
    :longitude => row['longitude']
  })

end

seed_writer.finish

There is also a SeedFu::Writer::Seed in case you prefere the seed() syntax over the seen_many() syntax. Easy-peasy.

• Thanks to Matthew Beale for his great work in adding the writer, making it faster and better.

Copyright © 2008-2009 Michael Bleigh released under the MIT license