Last Updated: 2022-12-01
After about 10 years of maintaining my app, it got to the point where I had perhaps 100's of migration files in my project.
Therefore on "Sep 2019" I removed most of these (already migrated) migrations.
Some time later, when I recreated my database locally, the command for migrating (
rake db:migrate) failed.
This was because one of the surviving migrations was 20181023152914updateusers.rb, assumed no-longer existent tables were present
def change change_column :users, :subscribed, :boolean, default: true end
I was able to get around this issue in Rails by migrating the database from the
$ rake db:schema:load. But it was still annoying to break the
So, my lesson here is: Instead of deleting migrations outright, create a new
create_current_state that contains everything from the
schema up to this point.
NB: I need to be careful here to avoid losing data when this migration is run in
production, therefore I should get rid of any
force: true statements. Then I
would remove all the old migrations except this current one, e.g. with:
$ cd db/migrate/ && ls | grep -v '20100427083434_create_current_state.rb' | xargs rm
In the past, I made the mistake of including data transformation stuff in
migrations. This proved a bad idea because it slowed down future migrations (or
down-right broke them), and it introduced a dependency on old code (e.g. in
User) model, which increases maintenance costs and scope for error.
Instead use one-off scripts in rails/runners.