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ameingast / postgresql-simple-migration

PostgreSQL Schema Migrations for Haskell
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Can MigrationCommand be a Semigroup? #13

Closed expipiplus1 closed 7 years ago

expipiplus1 commented 7 years ago

Would it make sense to add another constructor to MigrationCommand. This constructor would be MigrationCommands :: [MigrationCommand] -> MigrationCommand. This would represent a sequence of commands to run one after another.

ameingast commented 7 years ago

What's a practical use case for this?

I'm asking, because the error semantics for executing a sequence of MigrationCommands are not obvious. E.g., what happens when you run the sequence [MigrationInitialization, MigrationFile, MigrationDirectory] and the execution blows up during MigrationFile? Is the initialisation rolled back? Do we need to execute the sequence in a database transaction? etc

expipiplus1 commented 7 years ago

postgresql-simple-migration seems to leave the transaction handling up to the user. I'd expect things to be rolled back if the user has wrapped things in a transaction.

I'd expect it to work as though all the commands were written out to files in a directory and MigrationDirectory was called there. MigrationDirectory is already a way of running a sequence of commands.

ameingast commented 7 years ago

Alright, if you can come up with a solution I'll have a look and merge it in.

expipiplus1 commented 7 years ago

Thanks!

On Thu, Jan 26, 2017, 7:31 AM Andreas Meingast notifications@github.com wrote:

Closed #13 https://github.com/ameingast/postgresql-simple-migration/issues/13 via 6fe9957 https://github.com/ameingast/postgresql-simple-migration/commit/6fe995708d6c7ce5b050fc405cb3ab63ddef37cc .

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