Database Specific Migration Code [duplicate]

Answer 1

Your migration has access to a database connection in connection and the connection has an adapter_name method so you can just ask it what sort of connection it is:

def self.up
    case connection.adapter_name
    when 'PostgreSQL'
        # Do PostgreSQL stuff
    when 'MySQL'
        # Do MySQL stuff
    else
        # Blow up and catch on fire. Or silently ignore it depending on your needs.
    end
end

I'm not sure if I have the MySQL adapter name right but the technique is sound and you can easily check the MySQL adapter name yourself.