activerecord: Initialize Migration with version from MigrationProxy.

[dylanahsmith]

Problem

When running migrations with rake db:migrate, notice how the output to standard output looks like the following.

==  CreateUserTable: migrating ================================================
==  CreateUserTable: migrated (0.0000s) =======================================

This output is done through Migration#announce, delegated from MigrationProxy, as follows

From
https://github.com/rails/rails/blob/master/activerecord/lib/active_record/migration.rb#L596

    def announce(message)
      text = "#{version} #{name}: #{message}"
      length = [0, 75 - text.length].max
      write "== %s %s" % [text, "=" * length]
    end

The output is supposed to include a version, but the version is always nil within the migration. The MigrationProxy has the version, but initializes the Migration with the default parameters (i.e. version = nil)

This missing version can also be a problem when trying to use the version within a migration. Our use case for doing this is to update a schema_migrations table on each shard, so a migration that succeeds on one shard, then fails on another, can be retried only on the shards it still needs to run on.

Solution

Initialize the Migration loaded from a MigrationProxy with the version.

Backport

This can be cherry-picked without conflict onto the 4-0-stable or 3-2-stable branch.

[carlosantoniodasilva]

Any way to provide a test case so that we can be safe it won't happen again in the future? Thanks for the detailed explanation.

[dylanahsmith]

The migration itself is not exposed on the MigrationProxy, so I just created a migration that raised if the version was incorrect as a test.

[rafaelfranca]

We don't need the assert_nothing_raised. If something is raised the test will fail.

[dylanahsmith]

removed the assert_nothing_raised

[arthurnn]

❤️ 💚 💜 💛
👍

[arthurnn]

@dylanahsmith Can you add a changelog for this?

[kuldeepaggarwal]

👍

[steverob]

Superb. 👍

[dylanahsmith]

Added an active record changelog entry.