Set a default value for Stage lockable and make it non-nullable

[joshlory]

I ran into this in 03c1d43. See: https://robots.thoughtbot.com/avoid-the-threestate-boolean-problem.

irb(main):015:0> Script.first.stages.count
  Script Load (0.7ms)  SELECT  `scripts`.* FROM `scripts` ORDER BY `scripts`.`id` ASC LIMIT 1
   (0.5ms)  SELECT COUNT(*) FROM `stages` WHERE `stages`.`script_id` = 1
=> 20
irb(main):013:0> Script.first.stages.where(lockable: true)
  Script Load (0.9ms)  SELECT  `scripts`.* FROM `scripts` ORDER BY `scripts`.`id` ASC LIMIT 1
  Stage Load (0.6ms)  SELECT `stages`.* FROM `stages` WHERE `stages`.`script_id` = 1 AND `stages`.`lockable` = 1 ORDER BY absolute_position ASC
=> #<ActiveRecord::AssociationRelation []>
irb(main):013:0> Script.first.stages.where(lockable: false)
  Script Load (0.9ms)  SELECT  `scripts`.* FROM `scripts` ORDER BY `scripts`.`id` ASC LIMIT 1
  Stage Load (0.6ms)  SELECT `stages`.* FROM `stages` WHERE `stages`.`script_id` = 1 AND `stages`.`lockable` = 0 ORDER BY absolute_position ASC
=> #<ActiveRecord::AssociationRelation []>

First make the column non-nullable (setting a default value for NULL entries), then set the column default in a reversible way. Verified this migration can be rolled back:

$ rake db:migrate
== 20170508234535 ChangeLockableOnStage: migrating ============================
-- change_column_null(:stages, :lockable, false, false)
   -> 0.0583s
-- change_column_default(:stages, :lockable, {:from=>nil, :to=>false})
   -> 0.0180s
== 20170508234535 ChangeLockableOnStage: migrated (0.0765s) ===================

Annotated (1): app/models/stage.rb

$ rake db:rollback STEP=1
Ignoring db/schema_cache.dump because it has expired. The current schema version is 20170508234535, but the one in the cache is 20170505231542.
== 20170508234535 ChangeLockableOnStage: reverting ============================
-- change_column_default(:stages, :lockable, {:from=>false, :to=>nil})
   -> 0.0371s
-- change_column_null(:stages, :lockable, true, false)
   -> 0.0343s
== 20170508234535 ChangeLockableOnStage: reverted (0.0772s) ===================

Annotated (1): app/models/stage.rb

[ashercodeorg]

Q: Should the order of these two be reversed?

[joshlory]

It shouldn't matter, since the 4th param of change_column_null specifies the default value for NULL entries (false). I believe even if I swap the order, the 4th param is still needed.

[ashercodeorg]

Given the !!, can the comparison to true on line 595 be simplified (removed)?