如何在使用MySQL的Yii2迁移中实现AUTO_INCREMENT ?

I have created a yii2 (v2.0.6) migration for a simple MySQL (v5.6.21) table. Everything works, except that I cannot figure out how to AUTO_INCREMENT the primary key. The problem seems to be that I am using a small integer rather than the more standard long integer datatype. Here is my migration code:I have created a yii2 (v2.0.6) migration for a