python data_error ai_generated true

sqlalchemy.exc.PendingRollbackError: This Session's transaction has been rolled back due to a previous exception during flush

ID: python/pytest-sqlalchemy-session-scope-leak

Also available as: JSON · Markdown · 中文
80%Fix Rate
87%Confidence
0Evidence
2025-07-15First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
2.0.x active — — —

Root Cause

A session-scoped SQLAlchemy Session fixture reused across tests leaves a failed transaction after one test raises. Subsequent tests hit the same session in a pending-rollback state.

generic

中文

session 作用域的 SQLAlchemy Session fixture 跨测试复用；某测试抛异常后事务失败，后续测试使用同一 session 时处于待回滚状态。

Workarounds

  1. 94% success 
    @pytest.fixture
def db_session(engine):
    conn = engine.connect()
    trans = conn.begin()
    session = Session(bind=conn, join_transaction_mode='create_savepoint')
    yield session
    session.close()
    trans.rollback()
    conn.close()
  2. 90% success 
    @pytest.fixture
def session(engine):
    s = Session(engine)
    yield s
    s.rollback()
    s.close()

Dead Ends

Common approaches that don't work:

  1. 70% fail

    Doesn't isolate data written before the error; tests still see dirty state from previous tests.

  2. 85% fail

    Pool size is unrelated to transaction state; the pending rollback persists on the same session object.