http://laravel.com/docs/4.2/eloquent#dynamic-属性
class Phone extends Eloquent {
public function user()
{
return $this->belongsTo('User');
}
}
$phone = Phone::find(1);
现在，如果我做这样的事情：
echo $phone->user->email;
echo $phone->user->name;
echo $phone->user->nickname;
每次我使用->user动态属性时，Eloquent会调用数据库吗？或者这是否足够智能，可以在第一次调用时缓存用户？
在您的示例中，$phone对象上的user属性将延迟加载，但只加载一次。
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load方法手动重新加载关系。
以下代码举例说明：
$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);