Add an auto_increment column in Magento setup script without using SQL - magento

Question

Previously I asked how to ALTER TABLE in Magento setup script without using SQL. There, Ivan gave an excellent answer which I still refer to even now.
However I have yet to discover how to use Varien_Db_Ddl_Table::addColumn() to specify an auto_increment column. I think it has something to do with an option called identity but so far have had no luck.
Is this even possible or is that functionality incomplete?

Answer 1

One can create an autoincrement column like that (at least since Magento 1.6, maybe even earlier):
/** #var $table Varien_Db_Ddl_Table */
$table->addColumn( 'id', Varien_Db_Ddl_Table::TYPE_INTEGER, null, array(
'auto_increment' => true,
'unsigned' => true,
'nullable' => false,
'primary' => true,
), 'ID' );
Instead of "auto_increment", one may also use the keyword "identity".

Answer 2

I think that's something that hasn't been implemented yet.
If you look at the source to addColumn, you can see it looks for a identity/auto_increment option and sets an IDENTITY attribute on the internal column representation.
#File: lib/Varien/Db/Ddl/Table.php
if (!empty($options['identity']) || !empty($options['auto_increment'])) {
$identity = true;
}
$upperName = strtoupper($name);
$this->_columns[$upperName] = array(
'COLUMN_NAME' => $name,
'COLUMN_TYPE' => $type,
'COLUMN_POSITION' => $position,
'DATA_TYPE' => $type,
'DEFAULT' => $default,
'NULLABLE' => $nullable,
'LENGTH' => $length,
'SCALE' => $scale,
'PRECISION' => $precision,
'UNSIGNED' => $unsigned,
'PRIMARY' => $primary,
'PRIMARY_POSITION' => $primaryPosition,
'IDENTITY' => $identity
);
However, if you look at the createTable method on the connection object
#File: lib/Varien/Db/Adapter/Pdo/Mysql.php
public function createTable(Varien_Db_Ddl_Table $table)
{
$sqlFragment = array_merge(
$this->_getColumnsDefinition($table),
$this->_getIndexesDefinition($table),
$this->_getForeignKeysDefinition($table)
);
$tableOptions = $this->_getOptionsDefination($table);
$sql = sprintf("CREATE TABLE %s (\n%s\n) %s",
$this->quoteIdentifier($table->getName()),
implode(",\n", $sqlFragment),
implode(" ", $tableOptions));
return $this->query($sql);
}
you can see _getColumnsDefinition, _getIndexesDefinition, and _getForeignKeysDefinition are used to create a CREATE SQL fragment. None of these methods make any reference to identity or auto_increment, nor do they appear to generate any sql that would create an auto increment.
The only possible candidates in this class are
/**
* Autoincrement for bind value
*
* #var int
*/
protected $_bindIncrement = 0;
which is used to control the increment number for a PDO bound parameter (nothing to do with auto_increment).
There's also a mention of auto_increment here
protected function _getOptionsDefination(Varien_Db_Ddl_Table $table)
{
$definition = array();
$tableProps = array(
'type' => 'ENGINE=%s',
'checksum' => 'CHECKSUM=%d',
'auto_increment' => 'AUTO_INCREMENT=%d',
'avg_row_length' => 'AVG_ROW_LENGTH=%d',
'comment' => 'COMMENT=\'%s\'',
'max_rows' => 'MAX_ROWS=%d',
'min_rows' => 'MIN_ROWS=%d',
'delay_key_write' => 'DELAY_KEY_WRITE=%d',
'row_format' => 'row_format=%s',
'charset' => 'charset=%s',
'collate' => 'COLLATE=%s'
);
foreach ($tableProps as $key => $mask) {
$v = $table->getOption($key);
if (!is_null($v)) {
$definition[] = sprintf($mask, $v);
}
}
return $definition;
}
but this is used to process options set on the table. This auto_increment controls the table AUTO_INCREMENT options, which can be used to control which integer an AUTO_INCREMENT starts at.