Modifying old Rails migrations then adding a new migration that calls the old ones

Question

MySQL 5.7 began failing old migrations that set a default for columns of type text.

After editing the migration, dropping the development db and re-running all migrations, all worked fine in development.

For production:

1. Is my below understanding correct? Is this the main and/or only issue (besides editing old migrations being frowned upon)

The issue to look out for is that since you can't drop a production db, these migrations will not be run and not reflected in db/schema.rb. As a result, your code will be error prone because it was written to work with a slightly different schema in development.

2. My solution is to essentially force the migration to re-run by calling its up method in a new migration. (See below code). Is this a reasonable solution? ie. Will it work in all cases (no critical downfalls).

This is the original migration, made years ago in Rails 2

class AddZipWarpableResHistory < ActiveRecord::Migration[5.2]
  def self.up
    add_column :warpables, :history, :text, :default => "", :null => false
    add_column :warpables, :cm_per_pixel, :float, :default => 0, :null => false

    Warpable.find(:all).each do |w|
      r = w.get_cm_per_pixel
      w.cm_per_pixel = r if r != nil
      w.save
    end

  end

  def self.down
    remove_column :warpables, :history
    remove_column :warpables, :cm_per_pixel
  end
end

after edits (only including the edited lines below) in Rails 5

class AddZipWarpableResHistory < ActiveRecord::Migration[5.2]
  def self.up
    add_column :warpables, :history, :text, :null => false
    
    Warpable.all.each do |w|  # edited this bc find(:all) was broken as well
      r = w.get_cm_per_pixel
      w.cm_per_pixel = r if r != nil
      w.save
    end
  end
end

new migration to ensure it works in production:

• Note that none of the changes in that migration have any subsequent changes in other migrations before this one to account for

require_relative '20111005211631_add_zip_warpable_res_history'

class EnsureNoWarpableCorruption < ActiveRecord::Migration[5.2]
  def self.up
    AddZipWarpableResHistory.down
    AddZipWarpableResHistory.up

    msg = 'MySQL 5.7 began throwing errors on migrations that set a default for columns of type text.' + 
          'We edited that migration and rerun it here to ensure no data corruption in production'
    
    change_table_comment(:warpables, msg)
  end

  def self.down
    raise ActiveRecord::IrreversibleMigration
  end
end

3. Would just editing the production DB manually in MySQL before merging this be an alternative solution if the model code wasn't updated as well?

• MySQL doesn't support transactional migrations. Is this the simple solution when working with other databases?

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Notes

• I didn't execute SQL directly because then we would probably need to start storing db/structure.sql instead of db/schema.rb.

• I didn't try to fix any model code or other logic.