May 09, 2025

Let's say you git check feature1

Then you run a migration that creates a table. 

Then you git check feature2

Ideally you'd remember to rails db:rollback before switching to that branch, but you forgot or maybe you spent some time creating some good test data already and don't want to remove it. 

In the feature2 branch, you've already run some migrations and the developer forgot to add a column, so he rolled back, add the column, then force pushed the branch. Now you don't have the new column and you can't run the migration because rails thinks it already ran it. And if you try to rollback, you'll get 

rails db:rollback

ActiveRecord::UnknownMigrationVersionError:  (ActiveRecord::UnknownMigrationVersionError)

No migration with version number 20250303155013.

Because that migration is in another branch. You could create an empty migration with that number maybe?? Or today I learned you can do this:

rails db:migrate:status

   up     20241217201044  Create ai tutor messages
   up     20250220155121  ********** NO FILE **********
   up     20250224095708  ********** NO FILE **********
   up     20250303133136  ********** NO FILE **********
   up     20250303135434  ********** NO FILE **********
   up     20250303155013  ********** NO FILE **********

Which allows you to see what the database thinks has been migrated and what versions have a migrate file. 

So now can you can clean up the migrations with no files.

delete from schema_migrations where version > '2024';

Now I can rollback.

Update: 5 min later 

You can also:

rails db:migrate:down VERSION=20241217201044

I'd tried step before, but it doesn't work if your migrations are broken like described above.