Proposal: Work with the related models in AR like one-entity.

I don't know how to name it, I just try to explain by example.
We have models like this:

class User extends ActiveRecord
{
    // ...
    public function getFiles(): ActiveQuery
    {
        return $this->hasMany(UserFile::class, ['id' => 'file_id']);
    }
    // ...
}

class UserFile extends ActiveRecord
{
    // ...
}

And we need to load/save/update/etc User and UserFiles in one transaction because we wanna has integrity DB.

What we do: https://www.yiiframework.com/doc/guide/2.0/en/input-multiple-models
But it is not a right way to save/update integrity models.

Yes, we can use AR/DB transaction methods from Yii but I think must work by default when we work with related models/data.

And also we type same code for save related models.

My proposal:

When we wanna create/update/save/delete related models we must use eager-loading for get models:

User::find()-> with(['files'])->one();

... forms and etc.

And when we get data by request from browser we just use load function:

$user->load(Yii::$app->request->post())

And this function load all related models if it was loaded. And after that - validate & save all models like one Entity.

BUT: For security reason we must allow to work like this only for one "Entity".
What I mean - UserFiles without User doesn't have any value, User and UserFiles - it is one Entity. And for this we must have agreement that - If a model name has parent name (UserFiles has User) it must interpreted like one-single entity.

Thanks. I will be grateful for the reasoned criticism and additions.
And yes, I'm ready to implement this if it was be accepted.

UPDATE (2019-05-22):

1. dependent models by model name (User -> [User]File) - reject
   My proposal - use static method that return array where key is relation name and value is FQCN for dependent model
   Example ['files' => 'app/models/UserFile']
2. eager-loading isn't necessary

Start with the proposal's ActiveRecord relation-loading and load/save examples, then review the linked Yii multiple-model input guidance and transaction methods. Done would require an accepted design for safely loading, validating, and persisting related models as one entity, with tests covering the agreed behavior.