List columns within the method for a migration

[zunda]

I tried creating a new server after a while and saw the exception below while running rake db:migrate for the first time. This change is to avoid this exception.

NoMethodError: undefined method `perform' for nil:NilClass
.../vendor/bundle/ruby/2.6.0/gems/strong_migrations-0.4.1/lib/strong_migrations/migration.rb:14:in `method_missing'
.../vendor/bundle/ruby/2.6.0/gems/activerecord-5.2.3/lib/active_record/migration.rb:604:in `method_missing'
.../db/migrate/20170918125918_ids_to_bigints.rb:69:in `<class:IdsToBigints>'
.../db/migrate/20170918125918_ids_to_bigints.rb:3:in `<top (required)>'

[ClearlyClaire]

It looks ok to me, but I'm not sure how that's changing anything?

[zunda]

It seems to me that the exception is raised at migration.rb:14. in the definition of method_missing(method, *args) method:

      @checker.perform(method, *args) do

before the instance variable @checker is initialized. While I haven't fully followed it, it seems to me happening when table_exists?(:deprecated_preview_cards) is evaluated while the file is being loaded.

This change is to defer the evaluation until when up or down method is called so that @checker will have been initialized.