From 20a136e2a1e805ac7eac665ad16b385e6a9affdb Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Mon, 5 Oct 2020 08:08:47 -0500
Subject: [PATCH] Avoid event data serialization during recorder that we throw
 away (#41217)

We currently serialize the event data for state change events
and then replace it because we save the state in the states table.
Since the old state and new state are both contains in the event
the cost of serializing the data has a noticable impact when there
are many state changed events.
---
 homeassistant/components/recorder/__init__.py |  5 +++--
 homeassistant/components/recorder/models.py   |  4 ++--
 tests/components/recorder/test_models.py      | 14 ++++++++++++++
 3 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/homeassistant/components/recorder/__init__.py b/homeassistant/components/recorder/__init__.py
index 02a07bab628..5ecfad5d204 100644
--- a/homeassistant/components/recorder/__init__.py
+++ b/homeassistant/components/recorder/__init__.py
@@ -381,9 +381,10 @@ class Recorder(threading.Thread):
                     continue
 
             try:
-                dbevent = Events.from_event(event)
                 if event.event_type == EVENT_STATE_CHANGED:
-                    dbevent.event_data = "{}"
+                    dbevent = Events.from_event(event, event_data="{}")
+                else:
+                    dbevent = Events.from_event(event)
                 self.event_session.add(dbevent)
             except (TypeError, ValueError):
                 _LOGGER.warning("Event is not JSON serializable: %s", event)
diff --git a/homeassistant/components/recorder/models.py b/homeassistant/components/recorder/models.py
index 642407cf0c6..e0f733fbfa0 100644
--- a/homeassistant/components/recorder/models.py
+++ b/homeassistant/components/recorder/models.py
@@ -60,11 +60,11 @@ class Events(Base):  # type: ignore
     )
 
     @staticmethod
-    def from_event(event):
+    def from_event(event, event_data=None):
         """Create an event database object from a native event."""
         return Events(
             event_type=event.event_type,
-            event_data=json.dumps(event.data, cls=JSONEncoder),
+            event_data=event_data or json.dumps(event.data, cls=JSONEncoder),
             origin=str(event.origin),
             time_fired=event.time_fired,
             context_id=event.context.id,
diff --git a/tests/components/recorder/test_models.py b/tests/components/recorder/test_models.py
index bf659282e3e..c11fa8a692f 100644
--- a/tests/components/recorder/test_models.py
+++ b/tests/components/recorder/test_models.py
@@ -19,6 +19,7 @@ from homeassistant.const import EVENT_STATE_CHANGED
 import homeassistant.core as ha
 from homeassistant.exceptions import InvalidEntityFormatError
 from homeassistant.util import dt
+import homeassistant.util.dt as dt_util
 
 ENGINE = None
 SESSION = None
@@ -241,3 +242,16 @@ async def test_process_timestamp_to_utc_isoformat():
         == "2016-07-09T21:31:00+00:00"
     )
     assert process_timestamp_to_utc_isoformat(None) is None
+
+
+async def test_event_to_db_model():
+    """Test we can round trip Event conversion."""
+    event = ha.Event(
+        "state_changed", {"some": "attr"}, ha.EventOrigin.local, dt_util.utcnow()
+    )
+    native = Events.from_event(event).to_native()
+    assert native == event
+
+    native = Events.from_event(event, event_data="{}").to_native()
+    event.data = {}
+    assert native == event