Add Migrations to a Rails Engine's Install Generator - ruby-on-rails

Question

In my rails 5 engine I want to include the installation of the engine's migrations with the custom install generator I have at:
myengine/lib/generators/myengine/install_generator.rb
This generator currently looks like this:
module Myengine
module Generators
class InstallGenerator < Rails::Generators::Base
source_root File.expand_path("../../templates", __FILE__)
desc "Creates a Myengine initializer and copys template files to your application."
def copy_initializer
template "myengine.rb", "config/initializers/myengine.rb"
end
end
end
end
When I add the engine to a rails app, instead of having to call:
rails g myengine:install
then
rails myengine:install:migrations
How can I add the creation of those migrations to the custom generator?

Answer 1

Fun question! And one that I hope I can answer. Let's say you have an engine named "Buttafly" and a generator living at:
#lib/generators/buttafly/install/install_generator.rb
At the top of your generator, require the 'date' library like so:
require 'date'
Then in the body of your generator, add a method definition like:
def copy_migrations
# get an array of the migrations in your engine's db/migrate/
# folder:
migrations = Dir[Buttafly::Engine.root.join("db/migrate/*.rb")]
migrations.each_with_index do |migration, i|
# The migrations will be created with the same timestamp if you
# create them all at once. So if you have more than one migration
# in your engine, add one second to the second migration's file
# timestamp and a third second to the third migration's timestamp
# and so on:
seconds = (DateTime.now.strftime("%S").to_i + i).to_s
seconds = seconds.to_s.length == 2 ? seconds : "0#{seconds}"
timestamp = (DateTime.now.strftime "%Y%m%d%H%M") + seconds
# get the filename from the engine migration minus the timestamp:
name = migration.split("/").split("_").last
# See if a the name of your engine migration is already in your
# host app's db/migrate folder:
if Rails.root.join("db/migrate/*#{name}").exist?
# do nothing:
puts "Migration #{name} has already been copied to your app"
else
# copy your engine migration over to the host app with a new
# timestamp:
copy_file m, "db/migrate/#{timestamp}_buttafly_#{name}"
end
end
end