Thursday, September 7, 2017
Hi Ben!
On Thursday, September 7, 2017 at 7:49:23 PM UTC+2, Ben Edwards wrote:
-- I can highly suggest the corresponding Rails Guide on this topic: http://edgeguides.rubyonrails.org/active_record_migrations.html
schema.rb contains the current structure of your database. When you migrate up or down, schema.rb is updated and will always reflect the latest state. You can also manually re-generate it by invoking the db:schema:dump rake task.
The individual migration files describe a change to your database (removing/adding columns, adding/removing tables,...). Each migration has a version number (which is a timestamp), and as soon as that migration is run (up), Rails writes a new row into the schema_migrations with the timestamp of the migration. When you down-migrate a migration, Rails deletes that row from the schema_migrations table.
Coming to your final question on how to best restore the state of your database, without the missing migration: If you don't have any important data in your database (i.e. it's just develop or test), I'd do a git reset --hard (which will give you a clean HEAD), and then invoke the db:structure:load rake task (which will delete the current structure of your DB and replace it with what's defined in your schema.rb).
On Thursday, September 7, 2017 at 7:49:23 PM UTC+2, Ben Edwards wrote:
Hi, ime trying to get my head around how these interact as I acidentely deleted a migration and had not commited it to git.
The migration is 'up'. So I did some research and it seems if I just delete the migration from the schema_migrations (and make sure the corresponding database object does not exist) will fix it. So I had a look at scema_migrations table and this got me wondering how rails knows if the migration is up or down, there is not status attribute on the table.So I did some more research and came across db/schema.rb, which rails used to work out if a migration is up or down. I looked in log/development.log to doble check what the migration was doing and found 'CREATE TABLE "create_report_upcoming_
events" so I checked db/schema.rb and sure enough there is a reference to the view. This is not domething I want and it has not been put into production. So it seems if I just delete the record from the scema_migrations table things will still be inconsistent.
So do I delete the row from schema_migrations and the reference to the view in db/schema.rb or will just deleting the migration from scema_migrations sufice?
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