유저 API N+1 쿼리 개선 (#27)

- Session 생성 시 간헐적으로 DB 와 통신에 실패하는 케이스를 대응하기 위해 retry 로직 추가
- 각 retry 마다 비동기적으로 대기하는 로직을 위해 get_db_session 을 async generator 로 변경
- UserRepository 의 get_users 에서 N+1 쿼리가 발생하는 문제를 개선

waffledotcom/src/apps/user/repositories.py

@@ -1,5 +1,5 @@
 from fastapi import Depends
-from sqlalchemy.orm import Session
+from sqlalchemy.orm import Session, joinedload
 
 from waffledotcom.src.apps.user.models import User
 from waffledotcom.src.database.connection import Transaction, get_db_session
@@ -15,7 +15,7 @@ def __init__(
         self.transaction = transaction
 
     def get_users(self) -> list[User]:
-        return self.session.query(User).all()
+        return self.session.query(User).options(joinedload(User.positions)).all()
 
     def get_user_by_id(self, user_id: int) -> User | None:
         return self.session.query(User).filter(User.id == user_id).first()

waffledotcom/src/database/connection.py

@@ -1,8 +1,10 @@
-from typing import Iterator
+import asyncio
+from collections.abc import AsyncIterator
 
 import sqlalchemy
 from fastapi import Depends
 from sqlalchemy import orm
+from sqlalchemy.exc import DatabaseError
 from sqlalchemy.orm.session import Session
 
 from waffledotcom.src.database.config import db_config
@@ -22,17 +24,24 @@ def __init__(self):
     def get_engine(self) -> sqlalchemy.Engine:
         return self._engine
 
-    def make_session(self) -> orm.Session:
-        session = self._session_maker()
-        return session
+    async def make_session(self) -> orm.Session:
+        exc = RuntimeError("이게 실행되면 버그이다.")
+        for _ in range(5):
+            try:
+                session = self._session_maker()
+                return session
+            except DatabaseError as e:
+                exc = e
+                await asyncio.sleep(1)
+        raise exc
 
     def teardown(self):
         orm.close_all_sessions()
         self._engine.dispose()
 
 
-def get_db_session() -> Iterator[orm.Session]:
-    session = DBSessionFactory().make_session()
+async def get_db_session() -> AsyncIterator[orm.Session]:
+    session = await DBSessionFactory().make_session()
 
     try:
         yield session