Yii和关系查询

Question

I have some tables that have foreign key references:

User -> Tech -> TechSchedule -> Location -> Customer

It seems that I can use the following query once to get any related data to the user. Consider the following query:

// load the user model
$model = User::model()->findByPk( Yii::app()->user->id );

// print
echo "<pre>", print_r( $model->attributes ), "</pre>";

// print more about the user
echo "<pre>", print_r( $model->Tech->TechSchedule[0]->Location->Customer ), "</pre>";

Prints out

Array
(
    [user_id] => 1
    [username] => someusername
    [password] => somepassword
    [salt] => somesalt
)

Customer Object
(
    [_new:CActiveRecord:private] => 
    [_attributes:CActiveRecord:private] => Array
        (
            [customer_id] => 14
            [more customer data...]
    )

[_related:CActiveRecord:private] => Array
    (
    )

[_c:CActiveRecord:private] => 
[_pk:CActiveRecord:private] => 14
[_alias:CActiveRecord:private] => t
[_errors:CModel:private] => Array
    (
    )

[_validators:CModel:private] => 
[_scenario:CModel:private] => update
[_e:CComponent:private] => 
[_m:CComponent:private] => 
)`

Is this normal behavior? If so, what would the purpose be of going through the hassle of writing relational queries, such as

$model = User::model()->with('Tech.TechSchedule.Location.Customer')->findByPk( Yii::app()->user->id );

Answer 1

When you do something like $model->Tech->TechSchedule[0]->Location->Customer, you will see that PHP will send a query to the database for each relation you try to access. In your case, that would probably amount to 4 different DB queries sent to the database. In many cases, you want to reduce the amount of times PHP queries the database because it is very costly (timewise).

If you do something like User::model()->with('...'), all those relations will be brought together with the User model. This might save you time if you know you will access that related data (less roundtrips to the DB) but you may bring unnecessary data if you just want to access data in the User table.

More information here(official docs)