aminghadersohi opened a new pull request, #39921:
URL: https://github.com/apache/superset/pull/39921
### SUMMARY
`get_chart_preview` intermittently raised `DetachedInstanceError` when a
`Slice` ORM object was loaded by `find_chart_by_identifier()` and then accessed
after a session expire inside `validate_chart_dataset()`.
Two changes:
1. **Eager session refresh** — call `db.session.refresh(chart)` immediately
after loading the `Slice` so all column attributes are populated in the
object's `__dict__` while the session is still active. This prevents
`DetachedInstanceError` when strategy classes later access lazy attributes.
2. **SQLAlchemy error handler** — add an explicit `except SQLAlchemyError`
block inside `_get_chart_preview_internal` so any residual session errors (e.g.
`DetachedInstanceError`) produce a clear `ChartError` with a "database session
error, please retry" message instead of propagating to the outer wrapper with a
generic message.
### BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF
N/A — backend-only fix.
### TESTING INSTRUCTIONS
1. Unit tests added in
`tests/unit_tests/mcp_service/chart/tool/test_get_chart_preview.py::TestDetachedInstanceError`:
- `test_session_refresh_called_after_chart_load` — verifies
`db.session.refresh()` is called once after chart lookup
- `test_detached_instance_error_returns_chart_error` — verifies
`DetachedInstanceError` raised inside the preview strategy returns a
`ChartError` (not an unhandled exception)
2. Run: `pytest
tests/unit_tests/mcp_service/chart/tool/test_get_chart_preview.py::TestDetachedInstanceError
-xvs`
### ADDITIONAL INFORMATION
- [ ] Has associated issue:
- [ ] Required feature flags:
- [ ] Changes UI
- [ ] Includes DB Migration
- [ ] Introduces new feature or API
- [ ] Removes existing feature or API
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