多次调用Eloquent动态属性会多次访问数据库吗？

Question

http://laravel.com/docs/4.2/eloquent#dynamic-properties

class Phone extends Eloquent {

    public function user()
    {
        return $this->belongsTo('User');
    }

}

$phone = Phone::find(1);

现在,如果我然后做这样的事情:

echo $phone->user->email;
echo $phone->user->name;
echo $phone->user->nickname;

每当我使用->user动态属性时,Eloquent是否会进行数据库调用？或者这是否足够聪明,可以在第一次通话时缓存用户？

Answer 1

在您的示例中,对象user上的$phone属性将是延迟加载的,但它只会加载一次.

还要记住,一旦加载了对象,它就不会反映对基础表的任何更改,除非您使用该load方法手动重新加载关系.

以下代码说明了该示例:

$phone = Phone::find(1);

// first use of user attribute triggers lazy load
echo $phone->user->email;

// get that user outta here.
User::destroy($phone->user->id);

// echoes the name just fine, even though the record doesn't exist anymore
echo $phone->user->name;

// manually reload the relationship
$phone->load('user');

// now will show null, since the user was deleted and the relationship was reloaded
var_export($phone->user);