In Yii3, validation rules are not part of the model - special form-class must be created. In Yii2 you didn't need the form-class for model-driven (db-driven) forms.
## ActiveRecord
Example of usage is in the following files. ActiveRecord combines 2 classes: Entity + Repository = data and DB manipulation.
## JS client - Installable Vuejs3 PWA
If you create a REST API you may be interested in a JS frontend that will communicate with it using Ajax. Below you can peek into my very simple VueJS3 attempt. It is an installable PWA application that works in offline mode (=1 data transfer per day, not on every mouse click) and is meant for situations when customer does not have wifi everywhere. See my [Gitlab](https://gitlab.com/radin.cerny/vuejs3-pwa-demo-plus).