c9s
Listed in http://dev.mysql.com/doc/refman/5.0/en/information-functions.html
That way, we can simply fetch the config from class property without looking up the nested config structure.
the reason: mixin schema might need to modify the meta class of the baseModel, however it's hard to merge the entries defined in UserClass
``` $this->hasMany('items', OrderItemSchema::class, 'order_id', 'id') ``` where `id` could be `$this->getKeyField()` or get the primary key internally.
`alter table foo drop foreign key foo_ibfk_1;`