Yii Migrate 设置字段自增主键

...
public function safeUp()
{
    $this->createTable('area', [
        'id' => \yii\db\Schema::TYPE_PK,
        'name' => $this->string(20)->unique(),
    ]);
}
...

见 \vendor\yiisoft\yii2\db\QueryBuilder.php 的 1173 行: