Alphabetize schema.rb columns

I wrote previously about automated testing of database rollback scripts
in
rails
.
After running the rollback scripts, we verify our database schema by
comparing the schema.rb file from before the upgrade with the one after
rollback. The problem is that the columns for each table in schema.rb
seem to appear in the order that they were created, not in alphabetical
order. So, if a column is dropped and then re-added, it will move down
to the bottom of the list. For example, we start with a table like:

  create_table "foo", :force => true do |t|
    t.string "first"
    t.string "second"
  end

Now, version 6 drops the “a” column, and the rollback adds it back.
Then, the schema.rb file will look like:

  create_table "foo", :force => true do |t|
    t.string "second"
    t.string "first"
  end

In order to compare schema.rb files before and after upgrades, we wanted
to alphabetize the column list. We did this by monkey patching the
columns method on ActiveRecord::Base.connection. We only want to change
the columns method when dumping the schema. We do not want to change the
running application in any way. so we only run our monkey patch when
calling the db:schema:dump task. Our solution looks like:

task :'db:schema:dump' => :'db:alphabetize_columns'

task :'db:alphabetize_columns' do
  class << ActiveRecord::Base.connection
    alias_method :old_columns, :columns unless self.instance_methods.include?("old_columns")

    def columns(*args)
      old_columns(*args).sort_by(&:name)
    end
  end
end
Paul Gross

Paul Gross

I'm a lead software developer in Seattle working for Braintree Payments.

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