Rails share code between migrations (aka concerns)

Question

I have a few migrations within identical helpers

  private

  def add_earthdistance_index table_name, options = {}
    execute "CREATE INDEX %s_earthdistance_ix ON %s USING gist (ll_to_earth(%s, %s));" %
      [table_name, table_name, 'latitude', 'longitude']
  end

  def remove_earthdistance_index table_name
    execute "DROP INDEX %s_earthdistance_ix;" % [table_name]
  end

And I'm trying to avoid copy-paste them every time. Is there any way to share code between migrations without monkey-patching the base class? I want to find something like concerns for models.

score 8 · Answer 1 · answered Jul 03 '16 at 20:23

Solution

Add config.autoload_paths += Dir["#{config.root}/db/migrate/concerns/**/"] to config/application.rb

Create db/migrate/concerns/earthdistanceable.rb file within

module Earthdistanceable
  extend ActiveSupport::Concern

  def add_earthdistance_index table_name, options = {}
    execute "CREATE INDEX %s_earthdistance_ix ON %s USING gist (ll_to_earth(%s, %s));" %
      [table_name, table_name, 'latitude', 'longitude']
  end

  def remove_earthdistance_index table_name
    execute "DROP INDEX %s_earthdistance_ix;" % [table_name]
  end

end

Use it:

class CreateRequests < ActiveRecord::Migration[5.0]
  include Earthdistanceable

  def up
    ...
    add_earthdistance_index :requests
  end

  def down
    remove_earthdistance_index :requests

    drop_table :requests
  end

end

score 4 · Answer 2 · answered Jul 03 '16 at 19:50

4

I think you could do something like:

# lib/helper.rb
module Helper
  def always_used_on_migrations
    'this helps' 
  end
end

Migration

include Helper
class DoStuff < ActiveRecord::Migration
  def self.up
    p always_used_on_migrations
  end

  def self.down
    p always_used_on_migrations
  end
end

answered Jul 03 '16 at 19:50

fabriciofreitag

2,843
22
26

Nice. But too explicit for me. I'd like to find something like `concerns` for models. – Arsen Jul 03 '16 at 19:56
Oh okay, sorry if it didn't suit you. – fabriciofreitag Jul 03 '16 at 19:58
3

@Arsen: do you _know_ how concerns work? It's just a module that you include in a class. And a migration is just a class. It's the same thing as with models, literally. – Sergio Tulentsev Jul 03 '16 at 20:04
@SergioTulentsev I know now. Because I have just implemented it. – Arsen Jul 03 '16 at 20:05

Rails share code between migrations (aka concerns)

2 Answers2

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