atkpubsubdemo

A small demo showing how Atk4\Core hooks can be created to create some pub/sub style action handling. The motivation is to get logic what should happen after Model::save() or Model::delete() away from the Model hooks directly.

There is a small Broker implemented as singleton. The Models just publish() their events (e.g. Model::HOOK_AFTER_SAVE) to this broker. Other code can then subscribe() these events and act accordingly. In this sample repo, there are SampleController and YetAnotherController which subscribe.

See or run the test code for a simple example. It illustrates that ModelA is unaware of any additional logic which should happen when it is saved but just publishes its after save event to the Broker. The 2 Controllers subscribe the after save event and act accordingly.

The main benefits are:

• No control flow logic within the Model hooks. The scope of the model can focus on the model itself and does not need to know the complete logic of your application.
• This way, it is easier to split up an application into several repositories. As ModelA no longer needs to know what should happen when it is saved, this logic can easily be moved elsewhere if sensible.

Using it to split up an application in several repos

In this sample repo, the 2 Controllers SampleControllerand YetAnotherController reside within the same repository, but they could be in different repositories. A repository setup which splits the logic into several repos could look like this:

graph TD;
    A(Base Repo with Broker and Models) --> B(SomeOtherRepo);
    A(Base Repo with Broker and Models) --> C(YetAnotherRepo);
    B --> D(Application repo bringing all together);
    C --> D;

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How would it be without?

Without using this simple pub/sub system, ModelA::init() would typically have looked like this, containing all the additional logic (or direct calls to it) within HOOK_AFTER_SAVE, meaning ModelA needed to be aware of all the other actions that should happen when it was saved:

    protected function init(): void
    {
        parent::init();
        $this->addField('some_field', ['type' => 'integer']);
        $this->hasMany(ModelB::class, ['model' => [ModelB::class, 'theirField' => 'model_a_id']]);

        $this->onHook(
            Model::HOOK_AFTER_SAVE,
            function (self $entity, bool $isUpdate) {
                if ($entity->get('some_field') === 1) {
                    (new ModelB($entity->getModel()->getPersistence()))->createEntity()
                        ->set('model_a_id', $entity->getId())
                        ->set('name', 'Tina')
                        ->save();
                }
                elseif($entity->get('some_field') === 2) {
                    (new ModelB($entity->getModel()->getPersistence()))->createEntity()
                        ->set('model_a_id', $entity->getId())
                        ->set('name', 'Hans')
                        ->save();
                }
            }
        );
    }