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I created a rails application using scaffolding and migrated the database. and I committed a local repository by git commit -m "First commit" then I unrolled the database using rake db:rollback and the application stopped working.

I tried to undo using git checkout . but the application wasn't still working till I migrated the database again using rake db:migrate.

Why is this happening?

The Pianist
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2 Answers2

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Rails' migration mechanism checks for a specific table in your db which shows which migrations are applied to your db and which are pending migrations (from the files that are present but without an entry).

When you perform a db:migrate or a db:rollback this table is also updated.

The db files are not inside your repository (and shouldn't be), so you can not undo these changes by git.

You need to use the tools provided by the rake tasks.

Running a rake -T db will give you a full list of the tools you have to manipulate your migrations and db status.

xlembouras
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  • Git and db migrations are two methods of maintaining a version history in your application. Git is for code, db migrations are for your database. Your application will generally not work when your database schema is not in sync with your coded models. For instance, model `User` should have a table `users` which is created in a migration. If you add new columns to a table through a migration without running the migrations, you can not refer to these new properties without crashing your local application. – jaysqrd Jun 29 '14 at 21:06
  • So isn't every things stored in some files in my application root directory? So why my schema isn't returning back when I checkout .? – The Pianist Jun 30 '14 at 09:21
  • what we usually do is add the `db/structure.sql` to the repo, which describes the db state. When developing the app you usually run db:migrate after you pull new code or (especially if someone new enters the team) you reconstruct the database from that file with `db:create`. – xlembouras Jun 30 '14 at 09:27
  • the files in your app root, are not connected with your db, you need to manually restore/upgrade it after a checkout – xlembouras Jun 30 '14 at 09:29
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If you want to redo or change the migration you need to create another one, for more info check this.

emerak
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