abstract class `Athena::ORM::Migrations::AbstractMigration`
inherits `Reference` #

The parent type of every migration.

A migration applies one change to the database's schema or data in #up, and reverts it in #down, by adding the SQL to execute via #add_sql:

class App::Migrations::Version20261014120000 < AORM::Migrations::AbstractMigration
  def description : String
    "Add the users' email"
  end

  def up : Nil
    self.add_sql "ALTER TABLE users ADD email VARCHAR(255) DEFAULT NULL"
  end

  def down : Nil
    self.add_sql "ALTER TABLE users DROP email"
  end
end

A new instance is created each time the migration is executed, via .new with just the connection. A migration therefore can't define an #initialize that takes other arguments. Its SQL is executed once #up or #down returns, so #connection can be used to read the data the migration needs, but changes made through it aren't part of the migration's SQL.

Transactions#

Each migration runs in a transaction, see #transactional?. Some databases, such as MySQL and MariaDB, implicitly commit the transaction when a statement changes the schema, such as CREATE TABLE. Statements executed before such a statement can't be rolled back if a later one fails, so it's best to return false from #transactional? in migrations that change the schema on those databases.