fix: lazy load

src/adapter/postgres.py

@@ -135,7 +135,14 @@ class Postgres(DatabaseBase):
     async def add_external_channel_to_targets(
         self, external_channel_id: uuid.UUID, target_channel_ids: list[uuid.UUID]
     ) -> None:
-        external_channel = await self.session.get(domain.ExternalChannel, external_channel_id)
+        stmt = (
+            select(domain.ExternalChannel)
+            .where(domain.ExternalChannel.id == external_channel_id)
+            .options(selectinload(domain.ExternalChannel.target_channels))
+        )
+        result = await self.session.execute(stmt)
+        external_channel = result.scalar_one_or_none()
+
         if not external_channel:
             raise ValueError(f'ExternalChannel {external_channel_id} not found')
 
@@ -149,7 +156,14 @@ class Postgres(DatabaseBase):
     async def remove_external_channel_from_target(
         self, external_channel_id: uuid.UUID, target_channel_id: uuid.UUID
     ) -> None:
-        external_channel = await self.session.get(domain.ExternalChannel, external_channel_id)
+        stmt = (
+            select(domain.ExternalChannel)
+            .where(domain.ExternalChannel.id == external_channel_id)
+            .options(selectinload(domain.ExternalChannel.target_channels))
+        )
+        result = await self.session.execute(stmt)
+        external_channel = result.scalar_one_or_none()
+
         if not external_channel:
             raise ValueError(f'ExternalChannel {external_channel_id} not found')