b140d4d82a
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51 lines
1.9 KiB
Markdown
51 lines
1.9 KiB
Markdown
---
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id: fecad34a-4cc1-4f00-878c-393a9ecb5df0
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type: solution
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title: "pytest-asyncio SQLAlchemy async DB test fixture pattern"
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tags: [mantimon-tcg, pytest, pytest-asyncio, sqlalchemy, async, testing, pattern]
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importance: 0.8
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confidence: 0.8
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created: "2026-01-27T15:50:36.216118+00:00"
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updated: "2026-01-27T15:50:36.216118+00:00"
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---
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When testing SQLAlchemy async with pytest-asyncio, the fixture teardown runs in a DIFFERENT event loop than the test body, causing 'Future attached to different loop' errors on async cleanup.
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SOLUTION:
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1. Use sync psycopg2 for fixture setup/teardown operations (migrations, truncate)
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2. Create fresh NullPool engine per test (no connection reuse)
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3. Use TRUNCATE via sync psycopg2 in teardown instead of async rollback
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4. Suppress warnings for connection cleanup (harmless GC noise)
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KEY CODE (conftest.py):
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```python
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def truncate_all_tables():
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conn = psycopg2.connect(**DB_PARAMS)
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try:
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conn.autocommit = True
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with conn.cursor() as cur:
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for table in TABLES_TO_TRUNCATE:
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cur.execute(f'TRUNCATE TABLE {table} CASCADE')
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finally:
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conn.close()
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@pytest_asyncio.fixture
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async def db_session():
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engine = create_async_engine(URL, poolclass=pool.NullPool)
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session_factory = async_sessionmaker(engine, expire_on_commit=False)
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session = session_factory()
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try:
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yield session
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finally:
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try:
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await session.close()
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except RuntimeError:
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pass # Ignore event loop errors
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truncate_all_tables() # SYNC cleanup always works
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```
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ADDITIONAL NOTES:
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- When testing relationship loading (selectinload), must expire() the parent object first if children were added after initial load
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- ON DELETE SET NULL requires passive_deletes=True on relationship to let DB handle it
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- Suppress warnings in pyproject.toml: 'ignore:The garbage collector is trying to clean up:sqlalchemy.exc.SAWarning'
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