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Devices added after integration setup

Reasoning​

Like explained in the rule stale-devices, devices should be removed automatically when we can be sure that the device is not connected anymore. This rule explains the other side, once a new device is connected, we should automatically create the relevant entities for the device.

This makes the user experience better, since the user only adds the device to the integration, and it will automatically show up in Home Assistant.

Example implementation​

In the example below we use a coordinator to fetch all the data from the service. Every update _check_device will check if there are new devices to create entities for and add them to Home Assistant.

coordinator.py

class MyCoordinator(DataUpdateCoordinator[dict[str, MyDevice]]):
    """Class to manage fetching data."""

    def __init__(self, hass: HomeAssistant, client: MyClient) -> None:
        """Initialize coordinator."""
        super().__init__(
            hass,
            logger=LOGGER,
            name=DOMAIN,
            update_interval=timedelta(minutes=1),
        )
        self.client = client

    async def _async_update_data(self) -> dict[str, MyDevice]:
        try:
            return await self.client.get_data()
        except MyException as ex:
            raise UpdateFailed(f"The service is unavailable: {ex}")

sensor.py

async def async_setup_entry(
    hass: HomeAssistant,
    entry: MyConfigEntry,
    async_add_entities: AddEntitiesCallback,
) -> None:
    """Set up My integration from a config entry."""
    coordinator = entry.runtime_data

    known_devices: set[str] = set()

    def _check_device() -> None:
        current_devices = set(coordinator.data)
        new_devices = current_devices - known_devices
        if new_devices:
            known_devices.update(new_devices)
            async_add_entities([MySensor(coordinator, device_id) for device_id in new_devices])

    _check_device()
    entry.async_on_unload(
        coordinator.async_add_listener(_check_device)
    )

Exceptions​

There are no exceptions to this rule.