Add blog post for entry.runtime_data (#2160)

blog/2024-04-30-store-runtime-data-inside-config-entry.md

@@ -0,0 +1,49 @@
+---
+author: Marc Mueller
+authorURL: https://github.com/cdce8p
+title: "Store runtime data inside the config entry"
+---
+
+Integrations often need to set up and track custom data, such as coordinators, API connections, or code objects. Previously, those were all stored inside `hass.data`, which made tracking them difficult.
+
+With recent changes, it's now possible to use `entry.runtime_data` for that. The config entry is already available when setting up platforms and gets cleaned up automatically. No more deleting the key from `hass.data` after unloading.
+
+It also better supports type-checking. `ConfigEntry` is generic now, so passing the data type along is possible. Use a typed data structure like `dataclass` for that. To simplify the annotation, it's recommended to define a type alias for it.
+
+An example could look like this:
+```py
+# <integration>/__init__.py
+
+# The type alias needs to be suffixed with 'ConfigEntry'
+MyConfigEntry = ConfigEntry["MyData"]
+
+@dataclass
+class MyData:
+    client: MyClient
+    other_data: dict[str, Any]
+
+async def async_setup_entry(
+    hass: HomeAssistant,
+    entry: MyConfigEntry,  # use type alias instead of ConfigEntry
+) -> bool:
+    client = MyClient(...)
+    
+    # Assign the runtime_data
+    entry.runtime_data = MyData(client, {...})
+```
+
+```py
+# <integration>/switch.py
+
+from . import MyConfigEntry
+
+async def async_setup_entry(
+    hass: HomeAssistant,
+    entry: MyConfigEntry,  # use type alias instead of ConfigEntry
+    async_add_entities: AddEntitiesCallback,
+) -> None:
+    # Access the runtime data form the config entry
+    data = entry.runtime_data
+    
+    async_add_entities([MySwitch(data.client)])
+```