Initialise plant attributes at startup (#19315)

* Initialise plant attributes at startup

* Pvizeli review comments

* Martin review change

homeassistant/components/plant.py

@@ -105,9 +105,6 @@ async def async_setup(hass, config):
     for plant_name, plant_config in config[DOMAIN].items():
         _LOGGER.info("Added plant %s", plant_name)
         entity = Plant(plant_name, plant_config)
-        sensor_entity_ids = list(plant_config[CONF_SENSORS].values())
-        _LOGGER.debug("Subscribing to entity_ids %s", sensor_entity_ids)
-        async_track_state_change(hass, sensor_entity_ids, entity.state_changed)
         entities.append(entity)
 
     await component.async_add_entities(entities)
@@ -250,6 +247,14 @@ async def async_added_to_hass(self):
             # only use the database if it's configured
             self.hass.async_add_job(self._load_history_from_db)
 
+        async_track_state_change(self.hass, list(self._sensormap),
+                                 self.state_changed)
+
+        for entity_id in self._sensormap:
+            state = self.hass.states.get(entity_id)
+            if state is not None:
+                self.state_changed(entity_id, None, state)
+
     async def _load_history_from_db(self):
         """Load the history of the brightness values from the database.
 

tests/components/test_plant.py

@@ -86,6 +86,20 @@ def test_low_battery(self):
         assert sensor.state == 'problem'
         assert sensor.state_attributes['problem'] == 'battery low'
 
+    def test_initial_states(self):
+        """Test plant initialises attributes if sensor already exists."""
+        self.hass.states.set(MOISTURE_ENTITY, 5,
+                             {ATTR_UNIT_OF_MEASUREMENT: 'us/cm'})
+        plant_name = 'some_plant'
+        assert setup_component(self.hass, plant.DOMAIN, {
+            plant.DOMAIN: {
+                plant_name: GOOD_CONFIG
+            }
+        })
+        self.hass.block_till_done()
+        state = self.hass.states.get('plant.'+plant_name)
+        assert 5 == state.attributes[plant.READING_MOISTURE]
+
     def test_update_states(self):
         """Test updating the state of a sensor.