How to use yii2 hasone

There are two types of associations between tables in Yii2, which are used to specify the association between two models.

One-to-many: hasMany

One-to-one: hasOne (recommended learning: yii tutorial)

Return results: The return results of these two methods are yii\db\ActiveQuery objects

The first parameter: the class name of the associated model.

The second parameter: is an array, where the key is the attribute in the associated model and the value is the attribute in the current model.

Associated use

Now we get all the order information of a customer

$customer = Customer::findOne(1);  
$orders = $customer->orders; // 通过在Customer中定义的关联方法（getOrders()）来获取这个客户的所有的订单。

The above two lines of code will generate the following sql statement

SELECT * FROM customer WHERE id=1;  
SELECT * FROM order WHERE customer_id=1;

Association result caching

If the customer's order changes, we call it again

$orders = $customer->orders;

When you get the order again, you will find that there is no change. The reason is that the database will only be queried when $customer->orders is executed for the first time, and the results will be cached, and sql will not be executed during subsequent queries.

So what if I want to execute sql again? You can execute

unset($customer->orders);  
$customer->orders;

and then you can fetch data from the database.

Code Description:

// 执行sql语句: SELECT * FROM customer WHERE id=1  
$customer = Customer::findOne(1);  
//执行sql：SELECT * FROM order WHERE customer_id=1  
$orders1 = $customer->orders;  
//这个不会执行sql，直接使用上面的缓存结果  
$orders2 = $customer->orders;
//如果中间的用户订单有变化，我们就不能从缓存中获取，要unset掉
unset($customer->orders);  
$orders2 = $customer->orders;

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