fix: preserve _marimo_row_id when clamping table columns (#8029)
#8035
+62
−3
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## Summary When a table has more columns than `max_columns` (default 50), column clamping would exclude the `_marimo_row_id` column from the data sent to the frontend. Without this column, the frontend falls back to positional indices for row identification, which breaks selection after filtering — selecting a row returns data from the wrong row. ## Fix Always include `_marimo_row_id` in the selected columns when clamping, so the frontend can use stable row IDs for correct selection regardless of column count.
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Pull request overview
This PR fixes a critical bug where selecting rows in a filtered table with more than 50 columns would return data from the wrong rows. The root cause was that column clamping excluded the _marimo_row_id column, forcing the frontend to fall back to positional indices which broke after filtering.
Changes:
- Always include
_marimo_row_idin clamped column selection when the table has stable row IDs - Update existing tests to expect
max_columns + 1columns (accounting for_marimo_row_id) - Add comprehensive regression test that verifies selection works correctly with clamped columns and filtering
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| marimo/_plugins/ui/_impl/table.py | Modified column clamping logic to always include _marimo_row_id when present, ensuring frontend can use stable row IDs for selection |
| tests/_plugins/ui/_impl/test_table.py | Updated existing column clamping tests to account for _marimo_row_id column and added regression test verifying selection works correctly with clamped columns and filtering |
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Light2Dark
approved these changes
Jan 29, 2026
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Closes #8029
When a table has more columns than
max_columns(default 50), columnclamping would exclude the
_marimo_row_idcolumn from the data sentto the frontend. Without this column, the frontend falls back to
positional indices for row identification, which breaks selection after
filtering — selecting a row returns data from the wrong row.
Fix
Always include
_marimo_row_idin the selected columns when clamping,so the frontend can use stable row IDs for correct selection regardless
of column count.