Check whether you migrate up or down in Rails 3.1?

rubyonrails-talk
1

Hi!

In Rails 3.1 there is only one method for migrations called ‘change’.

I want to run some code in a migration only when migrating up, not down. Is that possible?

The issue I have is that this code is inside a migration file from Active Admin:

Create a default user

AdminUser.create!(:email => ‘admin@example.com’, :password => ‘password’, :password_confirmation => ‘password’)

So, when I try to migrate down this will fail because there is already a user present.

Any ideas?

Regards Linus

2

Hi!

In Rails 3.1 there is only one method for migrations called ‘change’.

Not exaclty. up and down still exist (but now instance methods instead of

class methods).

Google (“rails guide migrations”).

I want to run some code in a migration only when migrating up, not down. Is that possible?

Yes.

The issue I have is that this code is inside a migration file from Active Admin:

Create a default user

AdminUser.create!(:email => ‘admin@example.com’, :password => ‘password’, :password_confirmation => ‘password’)

So, when I try to migrate down this will fail because there is already a user present.

And what about:

def up

AdminUser.create!(:email => ‘admin@example.com’, :password => ‘password’, :password_confirmation => ‘password’)

end

def down

u = AdminUser.find_by_email(‘admin@example.com’)

u.destroy

end

Any ideas?

If the down migration is really impossible to do (which can happen;

e.g because you miss data to reset everything to the original state)

than you can raise ActiveRecord::IrreversibleMigration exception

in the down migration.

HTH,

Peter

3

I see.

Thank you very much Peter!

Regards

Linus