2 ideas for (optional?) rules

[John Bachir]

1. do not allow mixing transaction-allowed and transaction-not-allowed changes in one migration
2. do not allow more than one transaction-not-allowed change in one migration

This helps keep retries more robust and various problem-solving scenarios easier to deal with.

[Andrew Kane]

Hey @jjb, thanks for the suggestion. I don't want to support more checks that don't affect safety right now, so I think these are better as custom checks (maybe someone can create a gist for it).

[John Bachir]

Gotcha - sounds good - I didn't know about custom checks! Can a check access info about the other invoked methods in a migration? I didn't see anything in checks.rb but maybe I'm missing it. If not possible, will be a fun metaprogramming challenge 😈

[Andrew Kane]

You can keep track of previous method calls with:

method_calls = {}
StrongMigrations.add_check do |method, args|
  # your check code ...

  (method_calls[version] ||= []) << [method, args]
end

Edit: you can use version to differentiate between migrations

[John Bachir]

🤯

[John Bachir]

@ankane can't figure this out: how does one introspect if disable_ddl_transaction! is present?

[Andrew Kane]

add_check executes inside the migration context, so it'll be the same as inside the migration (self.class.disable_ddl_transaction).

Edit: That's also how/why version works, fwiw

[John Bachir]

came up with this 🎉 which I'll put in an initializer

thanks to having replaced myself with a (very small) script, i no longer have to bug my colleagues about this.

# this scenario can still happen with add_reference, we could inhibit that too
# https://github.com/ankane/strong_migrations/issues/202
strong_migrations_method_calls = {}
StrongMigrations.add_check do |method, args|
  next unless 20221104000000 < version

  host = connection.raw_connection.host
  db = connection.current_database
  strong_migrations_method_calls[host] ||= {}
  strong_migrations_method_calls[host][db] ||= {}
  strong_migrations_method_calls[host][db][version] ||= []
  strong_migrations_method_calls[host][db][version] << [method, args]

  if strong_migrations_method_calls[host][db][version].size > 1 && disable_ddl_transaction
    stop! <<~MESSAGE
      If a migration uses disable_ddl_transaction!, it must have only 1 operation.
      Put another way: if an operation requires disable_ddl_transaction!, then it must
      be in its own migration by itself.
      Note: because this is a disable_ddl_transaction! migration, the first operation in
      the migration probably succeeded, so if you try to run this again after fixing it you will get a
      "something already exists" error. So, you'll need to manually undo the first operation
      in this migration to get your dev environment back in good shape.
    MESSAGE
  end
end

[Andrew Kane]

Thanks for sharing