跨多个迁移重用代码：辅助模块和辅助方法

Question

. Answers to this question are eligible for a +50 reputation bounty. Timur Shtatland is looking for a to this question:

Please include an example of the relevant code: shared code (helper, concern, etc), migration that uses the shared code, and anything else that might be related (config if needed, etc).

I need to reuse the same method across many migrations. My goal is to avoid code duplication. I tried to do it as shown below, by putting the shared method into file lib/migration_helper.rb and using include MigrationHelper in the migrations that use the shared method.

Is there a more standard way of sharing code in different migrations?

In particular, I put the helper file into lib directory - is this the correct place?

## lib/migration_helper.rb

# Methods shared across migrations.

module MigrationHelper
  def my_shared_method
    # some shared code
  end
end

## db/migrate/do_something.rb

class DoSomething < ActiveRecord::Migration[5.2]
  include MigrationHelper
  # rubocop:disable Metrics/MethodLength
  def up
    # some code
    my_shared_method
  end
  # rubocop:enable Metrics/MethodLength

  def down
    # more code
    my_shared_method
  end

SEE ALSO:

I got a few ideas from these questions, but they do not fully answer my question:
Custom helper methods for Rails 3.2 Migrations
Rails share code between migrations (aka concerns)
Accessing custom helper methods in rails 3 migrations

This repo has examples of a much more complex version of what I want, with a whole hierarchy of helpers. I need a simpler solution:
https://gitlab.com/gitlab-org/gitlab-foss/blob/master/lib/gitlab/database/migration_helpers.rb
https://gitlab.com/gitlab-org/gitlab-foss/-/blob/master/db/migrate/20220808133824_add_timestamps_to_project_statistics.rb

Answer 1

just tested, works in rails 7 (and probably earlier version)

What you could do is:

1 - create your file/class kinda wherever

• app/lib/migration/something.rb
• db/concerns/something.rb
• ...

# db/concerns/create_column_alias.rb
module CreateColumnAlias
  def create_column_alias(*args)
    add_column(*args)
  end
end

2 - create an initializer to inject your new helper in the migrations classes (per this gist )

# initializers/extend_migration_with_custom_helpers.rb

require_relative "../../db/concerns/create_column_alias"

ActiveRecord::ConnectionAdapters::AbstractAdapter.send(:include, CreateColumnAlias)

3 - profit.

>$ bin/rails g my_migration

# db/migrate/123345456_my_migration.rb
class MyMigration < ActiveRecord::Migration[7.0]
  def change
    create_column_alias :tasks, :done, :boolean
  end
end