关于with()的用法

$topics = Post::find()->with('user', 'category')->limit(20)->where(['status' => 2])->orderBy(['created_at' => SORT_DESC])->all();
看到群主的代码里面有用到with()的方法, 发现这个方法大家用的蛮多的。希望能发个帖子，大家一起总结一下with()的用法
我先说一点，大家可以回复补充下总结哈。
with() 就是together的意思
Post这个类里面 要有  getUser() getCategory() 这个2个方法，这样就可以返回了组装在一起的数据了了。
下面是文档给出的3个example  哈哈哈

• The following are some usage examples:

// find customers together with their orders and country
Customer::find()->with('orders', 'country')->all();
// find customers together with their orders and the orders' shipping address
Customer::find()->with('orders.address')->all();
// find customers together with their country and orders of status 1
Customer::find()->with([
  'orders' => function (\yii\db\ActiveQuery $query) {
      $query->andWhere('status = 1');
  },
  'country',
])->all();

You can call with() multiple times. Each call will add relations to the existing ones. For example, the following two statements are equivalent:

Customer::find()->with('orders', 'country')->all();
Customer::find()->with('orders')->with('country')->all();