How to check if Rails code is running within a migration

Question

Is there some easy way to detect it?

I want to skip some code in the envirmonment.rb file when the rake/rails migrations are running.

Ammoniate

What do you mean with "is running in migration"? The question doesn't really make sense. :S – Ironwork

wow i dont get your question? yea what do u mean? – Tyrocidine

I don't known in envirmonment.rb whether my app is running from rake db:migrate or ruby script/server. If it's db:migrate, and i write some db query in envirmonment.rb, rails cannot do migrate because talbe does not exist yet. – Ammoniate

Answer 1

I had this problem in a legacy application I was maintaining. There were some observers that were interfering with migrations past a certain point, so I disabled them during migration by checking the application name and arguments

  # Activate observers that should always be running
  # config.active_record.observers = :cacher, :garbage_collector, :forum_observer# observers break a migrate from VERSION xxx - disable them for rake db:migrate
unless ( File.basename($0) == "rake" && ARGV.include?("db:migrate") )
  config.active_record.observers = :user_observer
end

Incorporating the comment below by @strw667, in Rails 6.1:

  # Activate observers that should always be running
  # config.active_record.observers = :cacher, :garbage_collector, :forum_observer# observers break a migrate from VERSION xxx - disable them for rake db:migrate
unless (File.basename($0) == "rake" &&  Rake.application.top_level_tasks == ["db:migrate")
  config.active_record.observers = :user_observer
end

Kalil

Great! Works just as well for optional gems that you only need in a rake task, but not in prod (and that may in fact interfere with your local script/server). Example: config.gem 'fsevents' if RAILS_ENV == 'development' && File.basename($0) == "rake" – Lillia

Nice. $0 gives you the file name from where application starts. For script/console it is irb ( in jruby it is jirb). – Humbuggery

Now that there are app preloaders like zeus, this trick may not work any more because $0 may not be "rake" (zeus lets you set aliases). – Appendant

It appears that this doesn't work any more since Rails 6.1 due to ARGV not being populated. Anyone know an alternative? c.f: #67124737 – Irby

In Rails 6.1 you can use File.basename($0) == "rake" && Rake.application.top_level_tasks == ["db:migrate"]. C.f: https://mcmap.net/q/176617/-how-do-i-detect-in-rails-if-i-am-running-a-rake-command – Irby

Answer 2

Use the following code to disable/enable specific code during migrations:

if !ARGV.include?("db:migrate") )
  config.active_record.observers = :user_observer
end

Neighbors

Answer 3

If you are running code that need the DB up to date I would suggest:

ActiveRecord::Base.connected? # This returns false if the db couldn't be connected to.
&& !ActiveRecord::Migrator.needs_migration? # This checks if a migration needs to run.

This will handle if you are running other db: tasks like db:setup.

Chitin

This is ActiveRecord::Base.connection.migration_context.needs_migration? now. https://mcmap.net/q/176618/-nomethoderror-undefined-method-needs_migration-39-for-activerecord-migrator-class – Chemotaxis

Answer 4

i think if u want to skip, just comment (#) on code.

or many choose on migration rake.

for example : rake db:migrate:up VERSION=2000123232 its mean , only 2000123232_create_article do migration.

or rake db:migrate VERSION=2000123232 mean start from after 2000123232

or rake db:migrate:down VERSION=2000123232

just rake help u can see what u need to rake.

Do you mean that?

Tyrocidine

Your answer is hard to understand (poor english) and you're not answering the question. – Jibe