Drupal 7 如何在复合密钥场景中构造MigrateSQLMap

如果表具有复合主键，我们如何实例化MigrateSQLMap？

由于MigrateSQLMap采用数组，您可以在源定义中设置多个字段：

// The source ID here is the one retrieved from each data item in the XML file, and
// used to identify specific items
$this->map = new MigrateSQLMap($this->machineName,
  array(
    'vendor_code' => array(
      'type' => 'varchar',
      'length' => 250,
      'not null' => TRUE,
    ),
    'client_code' => array(
      'type' => 'varchar',
      'length' => 250,
      'not null' => TRUE,
    ),
  ),
  MigrateDestinationEntityAPI::getKeySchema('vendor')
);

在上面的代码中，*供应商代码*和*客户代码*是复合密钥的组件