Create migration files from existing ActiveRecord models

Rakefile

# ActiveRecord migration by @bridgeutopia (http://www.blog.bridgeutopiaweb.com/post/activerecord-migrations-for-sinatra/)
# Added "rake reverse_migrate" to do reverse migration 

require 'rake'
require 'active_record'
require 'logger'
require 'yaml'

desc "Import DB"
task :import => :environment do
  url = ENV['URL'] or raise "No url specified, use URL="

  require 'rest_client'
  posts = YAML.load RestClient.get(url)

  posts.each do |post|
    DB[:posts] << post
  end
end

task :default => :dbsetup

task :loadconfig do
  DBconfig = YAML::load( File.open('db/mysql.yml') )['development']
end

desc "Setup db"
task :dbsetup => :loadconfig do
  create(DBconfig)
  migrate(DBconfig)
end

desc "Do migrations"
task :migrate => :loadconfig do
  migrate(DBconfig)
end

desc "Do reverse migrations"
task :reverse_migrate => :loadconfig do
  reverse_migrate(DBconfig)
end

def create( config )
  begin
    if config['adapter'] =~ /sqlite/
      if File.exist?(config['database'])
        $stderr.puts "#{config['database']} already exists"
      else
        begin
          # Create the SQLite database
          ActiveRecord::Base.establish_connection(config)
          ActiveRecord::Base.connection
        rescue
          $stderr.puts $!, *($!.backtrace)
          $stderr.puts "Couldn't create database for #{config.inspect}"
        end
      end
      return # Skip the else clause of begin/rescue
    else
      ActiveRecord::Base.establish_connection(config)
      ActiveRecord::Base.connection
    end
  rescue
    case config['adapter']
    when 'mysql'
      @charset = ENV['CHARSET'] || 'utf8'
      @collation = ENV['COLLATION'] || 'utf8_general_ci'
      begin
        ActiveRecord::Base.establish_connection(config.merge('database' => nil))
        ActiveRecord::Base.connection.create_database(config['database'], :charset => (config['charset'] || @charset), 
:collation => (config['collation'] || @collation))
        ActiveRecord::Base.establish_connection(config)
      rescue
        $stderr.puts "Couldn't create database for #{config.inspect}, charset: #{config['charset'] || @charset}, 
        collation: #{config['collation'] || @collation}"
      end
    when 'postgresql'
      @encoding = config[:encoding] || ENV['CHARSET'] || 'utf8'
      begin
        ActiveRecord::Base.establish_connection(config.merge('database' => 'postgres', 'schema_search_path' => 'public'))
        ActiveRecord::Base.connection.create_database(config['database'], config.merge('encoding' => @encoding))
        ActiveRecord::Base.establish_connection(config)
      rescue
        $stderr.puts $!, *($!.backtrace)
        $stderr.puts "Couldn't create database for #{config.inspect}"
      end
    end
  else
    $stderr.puts "#{config['database']} already exists"
  end
end

def migrate( config )
  ActiveRecord::Base.logger = Logger.new(STDOUT)
  ActiveRecord::Base.establish_connection(config)
  ActiveRecord::Migrator.migrate "db/migrate/"
end

def reverse_migrate( config )
  ActiveRecord::Base.logger = Logger.new(STDOUT)
  ActiveRecord::Base.establish_connection(config)
  
  # load model classes from directory
  Dir["./app/models/*.rb"].each do |file|
      require file
  end
  
  i = 0 
  tables = Hash[ActiveRecord::Base.send(:descendants).collect{|c| [c.table_name, c.name]}]
  
  tables.each do |table_name, class_name|
    m_name = table_name
    m_name = table_name.gsub("_","") if table_name.include?"_"
    filename = "db/migrate/#{"%04d"%i}_create_table_#{m_name}.rb"
    puts "creating migration #{filename}..."
    
    File.open(filename, 'w') do |f|
      
      f.write("class CreateTable#{m_name.capitalize} < ActiveRecord::Migration\n")
      f.write("  def up\n")
      f.write("    create_table :#{table_name} do |t|\n")
      
      columns = ActiveRecord::Base.connection.columns(table_name)
      columns.each do |col|
        f.write("      t.#{col.type} :#{col.name}\n") unless ['id','created_at','updated_at'].include?(col.name)
      end
      
      names = columns.collect{|c| c.name }
      f.write("\n      t.timestamps\n") if names.include?('created_at') && names.include?('updated_at')
      
      f.write("    end\n")
      f.write("  end\n")
      f.write("  def down\n")
      f.write("    drop_table :#{table_name}\n")
      f.write("  end\n")
      f.write("end") 
    end
    
    i+=1
  end
  
  puts "#{i.to_s} files created."
  puts "WARNING! change the database config if you are going to do \"rake migrate\" next, otherwise existing database(if any) will be overwritten"
  
end