fullfill graphql usertype; change db session to dep injection

app/db.py

@@ -21,6 +21,19 @@ if not DATABASE_URL:
 engine = create_engine(
     DATABASE_URL,
     pool_recycle=3600,
-    pool_pre_ping=True
+    pool_pre_ping=True,
+    connect_args={
+        "keepalives": 1,
+        "keepalives_idle": 30,
+        "keepalives_interval": 10,
+        "keepalives_count": 5
+    }
 )
-SessionLocal = sessionmaker(bind=engine)
+SessionLocal = sessionmaker(bind=engine)
+
+def get_db():
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()