Migrations in Rails Engine?

Question

I have multiple rails applications talking to the same backend and I'd like them to share some migrations.
I setup a rails engine (with enginex), I can share anything (controllers, views, models,...) but no migrations. I can't make it work !

I tried to create a file db/migrate/my_migration.rb but in my main application if I do :

  rake db:migrate 

It doesn't load them.

After some googling it appears there was some recent work on this and it seems this has been merge to rails master. I'm with rails 3.0.3 do you see any way to make this work ?

Thanks !

Answer 1

In rails 3.1, you can do it using this command, give that your engine name is example:

# Note that you append _engine to the name rake example_engine:install:migrations 

Answer 2

What i do, is add an InstallGenerator that will add the migrations to the Rails site itself. It has not quite the same behavior as the one you mentioned, but for now, for me, it is good enough.

A small how-to:

First, create the folder lib\generators\<your-gem-name>\install and inside that folder create a file called install_generator.rb with the following code:

require 'rails/generators/migration'  module YourGemName   module Generators     class InstallGenerator < ::Rails::Generators::Base       include Rails::Generators::Migration       source_root File.expand_path('../templates', __FILE__)       desc "add the migrations"        def self.next_migration_number(path)         unless @prev_migration_nr           @prev_migration_nr = Time.now.utc.strftime("%Y%m%d%H%M%S").to_i         else           @prev_migration_nr += 1         end         @prev_migration_nr.to_s       end        def copy_migrations         migration_template "create_something.rb", "db/migrate/create_something.rb"         migration_template "create_something_else.rb", "db/migrate/create_something_else.rb"       end     end   end end 

and inside the lib/generators/<your-gem-name>/install/templates add your two files containing the migrations, e.g. take the one named create_something.rb :

class CreateAbilities < ActiveRecord::Migration   def self.up     create_table :abilities do |t|       t.string  :name       t.string  :description       t.boolean :needs_extent             t.timestamps     end   end    def self.down     drop_table :abilities   end end 

Then, when your gem is added to some app, you can just do

rails g <your_gem_name>:install 

and that will add the migrations, and then you can just do rake db:migrate.

Hope this helps.