How to configure an extra/different migrations folder - ruby-on-rails

Question

A colleague and I are working in different projects that share some models. So, we are sharing the models through a git submodule.
Additionally, we'd like to be able to also share migrations:
In this way, my colleague's migrations would be in the folder db/migrate/other_db of my project.
How can I configure rails migrations to also run the migrations in this extra folder?

Answer 1

In your config file (config/application.rb for all environments or config/environments/$(environment).rb only for particular environment) add this line:
config.paths['db/migrate'] += 'db/migrate/other_db'
And if you want to change default 'db/migrate' path (config.paths['db/migrate'] is an array with one string 'db/migrate' by default), do this:
config.paths['db/migrate'] = ['db/my_migrate']
Here are default config.paths, which we also can change:
"app" => ["app"],
"app/assets" => ["app/assets"],
"app/controllers" => ["app/controllers"],
"app/helpers" => ["app/helpers"],
"app/models" => ["app/models"],
"app/mailers" => ["app/mailers"],
"app/views" => ["app/views"],
"lib" => ["lib"],
"lib/assets" => ["lib/assets"],
"lib/tasks" => ["lib/tasks"],
"config" => ["config"],
"config/environments" => ["config/environments"],
"config/initializers" => ["config/initializers"],
"config/locales" => ["config/locales"],
"config/routes" => ["config/routes.rb"],
"db" => ["db"],
"db/migrate" => ["db/migrate"],
"db/seeds" => ["db/seeds.rb"],
"vendor" => ["vendor"],
"vendor/assets" => ["vendor/assets"],
"vendor/plugins" => ["vendor/plugins"],
"config/database" => ["config/database.yml"],
"config/environment" => ["config/environment.rb"],
"lib/templates" => ["lib/templates"],
"log" => ["log/development.log"],
"public" => ["public"],
"public/javascripts" => ["public/javascripts"],
"public/stylesheets" => ["public/stylesheets"],
"tmp" => ["tmp"],

Answer 2

Update for Rails 5/6;
Rails 5 recommends setting additional migration paths in your config/database.yml file. It's very easy, see this example;
development:
migrations_paths:
- "db/migrate/other_db"
- "db/migrate/something_else"
ActiveRecord::Migrator.migrations_path= will be deprecated in Rails 6.

Answer 3

based on the answer by Swanand, we can write a migration to load the migrations in an external dir:
class MigrateMetadata < ActiveRecord::Migration
MIGRATIONS_PATH='db/migrate/metadata'
def self.up
Dir["#{MIGRATIONS_PATH}/[0-9]*_*.rb"].
sort.map{|filename|require filename}.flatten.
each{|class_name| const_get(class_name).up}
end
def self.down
Dir["#{MIGRATIONS_PATH}/[0-9]*_*.rb"].sort.reverse.
map{|filename|require filename}.flatten.
each{|class_name| const_get(class_name).down}
end
end

Answer 4

By the way, if you are building a gem to work with Rails, you can place a block like the following in your rail tie to add the gem's own migrations.
root = ... # the path to your gem
initializer :append_migrations do |app|
unless app.root.to_s.match root
app.config.paths["db/migrate"] << File.join(root, 'db/migrate')
end
end
There is no need to copy migrations from your gem with generators if you use this technique.
You can make a method to yield the root directory of your gem with some thing like this...
module MyGemName
def root
File.expand_path '../..', __FILE__
end
module_method :root
end
... in the file lib/my_gem_name.rb in your gem.

Answer 5

I do not know of a very clean way to do it, but the code that runs migrations looks something like:
#migrations ||= begin
files = Dir["#{#migrations_path}/[0-9]*_*.rb"]
migrations = files.inject([]) do |klasses, file|
version, name = file.scan(/([0-9]+)_([_a-z0-9]*).rb/).first
Where,
#migrations_path = 'db/migrate'
So if you change this to read from config file instead, it may work out in your favour. But as I said, this is definitely not a very clean way to do it.

Answer 6

Just add this initializer to your lib/engine.rb:
initializer 'your_engine_name.migrations' do |app|
config.paths['db/migrate'].expanded.each do |expanded_path|
app.config.paths['db/migrate'] << expanded_path
ActiveRecord::Migrator.migrations_paths << expanded_path
if Rake.application.top_level_tasks.empty?
ActiveRecord::Migration.check_pending! if ActiveRecord::Migrator.needs_migration?
end
end
end