When (if) to consolidate ActiveRecord migrations?

Question

As I move through the iterations on my application*(s) I accumulate migrations. As of just now there are 48 such files, spanning about 24 months' activity.

I'm considering taking my current schema.rb and making that the baseline.

I'm also considering deleting (subject to source control, of course) the existing migrations and creating a nice shiny new single migration from my my current schema? Migrations tend to like symbols, but rake db:schema:dump uses strings: should I care?

Does that seem sensible? If so, at what sort of interval would such an exercise make sense? If not, why not?

And am I missing some (rake?) task that would do this for me?

* In my case, all apps are Rails-based, but anything that uses ActiveRecord migrations would seem to fit the question.

Answer 1

Yes, this makes sense. There is a practice of consolidating migrations. To do this, simply copy the current schema into a migration, and delete all the earlier migrations. Then you have fewer files to manage, and the tests can run faster. You need to be careful doing this, especially if you have migrations running automatically on production. I generally replace a migration that I know everyone has run with the new schema one.

Other people have slightly different ways to do this.

I generally haven't done this until we had over 100 migrations, but we can hit this after a few months of development. As the project matures, though, migrations come less and less often, so you may not have to do it again.

This does go against a best practice: Once you check in a migration to source control, don't alter it. I make a rare exception if there is a bug in one, but this is quite rare (1 in 100 maybe). The reason is that once they are out in the wild, some people may have run them. They are recorded as being completed in the db. If you change them and check in a new version, other people will not get the benefit of the change. You can ask people to roll back certain changes, and re-run them, but that defeats the purpose of the automation. Done often, it becomes a mess. It's better left alone.