YII关联查询

以customer order两个表为例
//关联查询控制器中
$customer = Customer::find()->where('name'=>'zhangsan')->one();
$orders = $customer->hasmany('orders',['customer_id']=>'id')->asArray()->all();
$orders = $customer->hasmany(Order::className(),['customer_id']=>'id')->asArray()->all();

//customer模型中(优化)
public function getOrders(){
　　$orders = $this->hasmany('orders',['customer_id']=>'id')->asArray()->all();
}
//关联查询控制器中就可以这么写
$customer = Customer::find()->where('name'=>'zhangsan')->one();
$orders = $customer->getOrders();
//甚至可以这么写
$orders = $customer->orders;
//当获取未定义的类属性时会触发类的__get()魔术方法效果 YII会自动调用 getOrders()方法，而且会加上->all(),所以定义getOrders()时不能带上all()


//Order模型
public function getCustomer(){
　　$this->hasOne(Customer::className,['id'=>'customer_id'])->asArray();
}
//关联查询控制器中这么写
$order = Order::find()->where("id"=>'1')->one();
$customer = $order->customer;

/*
注意点
1.关联查询会被缓存
所以
$customer = Customer::find()->where('name'=>'zhangsan')->one();
unset($customer->orders);//清掉缓存
$order = $customer->orders;
2.关联查询的多次查询
$customers = Customer::find()->all();//select * from customer
foreach($customers as $customer){
$order = $customer->orders;//select * from order where customer_id = ...
}
//以上代码执行了101次sql查询，可以进行如下优化
$customers = Customer::find()->with('orders')->all();//select * from customer
foreach($customers as $customer){
$order = $customer->orders();//select * from order where customer_id in (...)
}//变成了2次查询

*/