Preserve every row in multi-file CSV responses - #577
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A file whose partition produces zero elements serializes to a bodiless CSV that pandas cannot parse, which failed the entire multi-file request. Such partitions now contribute no rows while every row from the remaining files is preserved.
CyMule
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July 21, 2026 00:46
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Shadow auto-approve: would auto-approve. Fixes a bug in CSV multi-file output by replacing an outer merge with row concatenation, preserving all rows and removing the unnamed index column. Change is bounded, well-tested, and clearly beneficial.
Re-trigger cubic
paulkarayan
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Jul 21, 2026
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nits:
- the CHANGELOG/description says results "union differing columns," but neither new test exercises files with different column sets. should be a quick llm addition
- line 753 item
paulkarayan
approved these changes
Jul 21, 2026
| if response.body.strip() | ||
| ] | ||
| if not frames: | ||
| return PlainTextResponse(responses[0].body) |
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nit:
do you need the response? PlainTextResponse("") seems like it would suit
…le-csv-rows # Conflicts: # CHANGELOG.md
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Summary
Why
CSV output for a multi-file request was built by outer-merging each file's
DataFrame into the previous one (
data.merge(resp_data, how="outer")). An outermerge joins on the intersection of columns, so identical rows across files
collapsed into a single row and legitimate duplicate rows were silently dropped
— most visibly when two uploads shared a filename. The merge also emitted the
row index as a leading unnamed column.
Impact
Multi-file CSV responses now retain every row from every file (including
duplicates and repeated filenames), union differing columns, and no longer
contain the extra unnamed index column. A file that produces no elements
contributes no rows rather than failing the whole request.
Validation
pytest test_general/api/test_app.py::test_output_format_csv_concatenates_multiple_files_without_index_column— 1 passedpytest test_general/api/test_app.py::test_output_format_csv_keeps_rows_when_one_file_has_no_elements— 1 passed