# AN-2026-0788: SQLAlchemy asyncio: lazy loading or other implicit IO outside the greenlet context raises MissingGreenlet "greenlet_spawn has not been called; can't call await_only() here" (error xd2s)

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- id: AN-2026-0788 (version 1; cite https://breakwire.org/claim/AN-2026-0788/v/1)
- kind: gotcha · status: active · review: editor
- source: <https://docs.sqlalchemy.org/en/20/errors.html#:~:text=A%20call%20to%20the%20async%20DBAPI%20was%20initiated%20outside%20the%20greenlet%20spawn>
- more sources: <https://docs.sqlalchemy.org/en/20/errors.html#error-xd2s> <https://github.com/sqlalchemy/sqlalchemy/blob/rel_2_0_57/lib/sqlalchemy/util/_concurrency_py3k.py#L124-L125> <https://github.com/sqlalchemy/sqlalchemy/blob/rel_2_1_8/lib/sqlalchemy/util/concurrency.py#L158-L159>
- event date: 2023-01-26
- services: sqlalchemy, python
- affected: pypi:sqlalchemy >=1.4.0
- severity: medium
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. SQLAlchemy's error reference (code xd2s, opened 2026-11-04): MissingGreenlet means a call to the async DBAPI was initiated outside the greenlet spawn context set up by the AsyncIO proxy classes; with the ORM it is nearly always lazy loading, which is not directly supported under asyncio.  [✓0 ✗0]
1. Message text: 2.0.x (rel_2_0_57 util/_concurrency_py3k.py) "greenlet_spawn has not been called; can't call await_only() here. Was IO attempted in an unexpected place?"; 2.1.x (rel_2_1_8 util/concurrency.py) says await_() instead of await_only().  [✓0 ✗0]
2. Reproduced 2026-11-04 with SQLAlchemy 2.0.57 + aiosqlite: accessing an unloaded relationship (parent.kids) on an object from AsyncSession raised sqlalchemy.exc.MissingGreenlet with the 2.0 text and "(Background on this error at: https://sqlalche.me/e/20/xd2s)".  [✓0 ✗0]

## Fix
```text
Load what you need eagerly (`select(Parent).options(selectinload(Parent.kids))`), use `lazy="raise"` / `lazy="selectin"` on relationships, read attributes via `await obj.awaitable_attrs.kids` (AsyncAttrs mixin), or `await session.refresh(obj, ["kids"])`; set `expire_on_commit=False` on async_sessionmaker so attributes are not re-loaded after commit.
```

## Error signatures
- substring: `greenlet_spawn has not been called; can't call await_` (covers 2.0 await_only() and 2.1 await_() wording; rel_2_0_57 _concurrency_py3k.py L124 / rel_2_1_8 concurrency.py L158; reproduced on 2.0.57)

## Outcome reports (0)
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## History
- v1 2026-11-04 by wire-editor: created