Given:

• running ActiveRecord migrations (provided by rails) alongside Mongo migrations (provided by this gem) within a single rails project.
• version == 202201010101 is a valid Active Record migration in your project.
• version == 202201010101 is NOT avalid Mongo migration in your project

Consider:

rake db:migrate VERSION=202201010101

Expected:

• The command should migrate the ActiveRecord data store to the 202201010101 version.
• The command should complete successfully with Mongo migrations being a no-op.

Actual:

• The command migrates the ActiveRecord data store to the 202201010101 version.
• The command errors because mongoid_rails_migrations is unable to find the 202201010101 version to migrate to.

My current workaround is a monkeypatch hack of Mongoid::Migrator.migrate to gracefully exit from mongo migrations. It's an ORM specific (ActiveRecord) solution. Ultimately I think the correct course of action is completely divorcing mongoid_rails_migrations from db:migrate and other default ActiveRecord rake tasks. However this is breaking behavior.

I'm happy to code up solutions to this if you have any other suggestions on reasonable/generic ways to solve this.

My monkey patch:

module Mongoid
  class Migrator
    class << self
      # override from https://github.com/adacosta/mongoid_rails_migrations/blob/2b8b1c98bac36d0332f7408c0ca2d8a9da308e37/lib/mongoid_rails_migrations/active_record_ext/migrations.rb#L205
      # This allows us to handle non-Mongo migration versions gracefully
      alias :old_migrate :migrate
      def migrate(migrations_path, target_version = nil)
        target_mongo_version_exists = Mongoid::Migrator.get_all_versions.index(target_version.to_i)
        target_rails_version_exists = ActiveRecord::Base.connection.migration_context.migrations.index { |migration| migration.version == target_version.to_i }

        if target_mongo_version_exists || (target_rails_version_exists.nil? && target_mongo_version_exists.nil?)
          old_migrate(migrations_path, target_version)
        elsif target_rails_version_exists
          # There is a valid migration here for Rails so just exit
          return
        else
          # we shouldn't actually ever hit this case as the rails migration rake task should error out before we get here
          # this is included for completeness and safety
          raise Mongoid::UnknownMigrationVersionError.new(target_version)
        end
      end
    end
  end
end

Note that this patch does not allow you to run mongoid migrations via db:migrate VERSION=. It simply allows you to run rails migrations without erroring. I wrote up separate rake tasks for mongoid migrate tasks targeting a version. I really didn't feel like patching ActiveRecord just to get this to work.