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I'm just learning Rails and have begun the section on database migrations. I built 2 migrations and both migrated up successfully. Migrating down, the latest migration, the one that runs first, failed because of a typo in my code. I fixed the typo but the migration continued to fail after that. I discovered the reason why was that the migrating down aborted half way through changes and then when I tried to migrate down again it failed because some of the changes had already been made and so column names were different and other issues like that. I ended up fixing it by fiddling with the schema_migrations table and manually rolling back my changes to a previous version and then migrating back up and down from there.

My question is, is there a way to tell Rails to run migrations in transaction mode and if the code fails, not to commit the transaction?

Jake Worth
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richbai90
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1 Answers1

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Rails will already run your migrations inside a transaction if your database supports it:

On databases that support transactions with statements that change the schema, migrations are wrapped in a transaction. If the database does not support this then when a migration fails the parts of it that succeeded will not be rolled back. You will have to rollback the changes that were made by hand.

It's up to you to use a database that respects transactions when performing schema changes. MySQL (as far as I know) doesn't, but Postgres absolutely does.

user229044
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  • Good to know. Thank you. – richbai90 Jun 14 '16 at 19:45
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    I'm using mariadb and it does support transactions. Is there a reason that it isn't working in this case? I'm using the mysql2 connector. – richbai90 Jun 14 '16 at 22:01
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    @richbai90 It depends on what you are doing in your migration. For example `alter table` statements do an implicit commit before executing the statement. See https://stackoverflow.com/questions/22806261/can-i-use-transactions-with-alter-table – tsauerwein Feb 11 '19 at 10:36