upgrade_model_storage (DataMapper::Migrations::DataObjectsAdapter)

    # File lib/dm-core/migrations.rb, line 115
          def upgrade_model_storage(model)
            properties = model.properties_with_subclasses(name)

            if success = create_model_storage(model)
              return properties
            end

            table_name = model.storage_name(name)

            with_connection do |connection|
              properties.map do |property|
                schema_hash = property_schema_hash(property)
                next if field_exists?(table_name, schema_hash[:name])

                statement = alter_table_add_column_statement(connection, table_name, schema_hash)
                command   = connection.create_command(statement)
                command.execute_non_query

                property
              end.compact
            end
          end