Example data migration using Veritas

veritas_migration.rb

class MyMigration < Veritas::Migration
  def call
    
    # Transformations
    # ---------------
    # 1) remove all columns except id, name and email
    # 2) rename user_id to id
    # 3) add a boolean active column, setting the default to false
    # 4) add a constraint on name where it must be between 1 and 100 characters

    schema[:users] = schema[:users].
      project([ :user_id, :name, :email ]).
      rename(:user_id => :id).
      extend   { |r| r.add([ :active, Boolean ], false) }.
      restrict { {r| r.name.length.gte(1).and(r.name.length.lte(100)) }

    # This generates the following DDL statement:
 
    # ALTER TABLE `users`
    #   DROP COLUMN `notes`,
    #   RENAME COLUMN `user_id` TO `id`,
    #   ADD COLUMN `active` BOOLEAN NOT NULL DEFAULT FALSE,
    #   CHANGE COLUMN `name` VARCHAR(100) NOT NULL CHECK (CHAR_LENGTH(`name`) >= 1)
  end
end

@postmodern I think that would be great for a higher level API. I'm thinking about a DSL that's block-based, where you specify the table, and then inside a block specify the transformations you want to apply. I will probably be thinking in terms of a few basic classes of operations:

• Adding
• Removing
• Changing
• Renaming

I would think that tables, columns and indexes should have one method for each of these actions. Even if the actual operations in the DB consist of multiple DDL statements, I would rather work at a higher level and just think in terms of the operation. I really don't want to make something that isn't an abstraction at all, and just a 1:1 mapping to some DDL statements ... if that's the case we'd be better off just using straight SQL.