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fix!: carry struct columns' full names through select, project and aggregate - #313
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…regate `select` computed its emit offset from the input's name count instead of its top-level field count, so over a struct column the output mapping pointed past the end of the projected fields. `select`, `project` and `aggregate` also kept only the first output name of each expression, dropping a struct column's nested names. They now keep the full depth-first `output_names` list, and a single `column(..., alias=...)` renames only the top-level field. Fixes substrait-io#311
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Check name Status Explanation Linked Issues check The changes satisfy issue #311.selectuses the input schema's top-level field count for emit mapping.selectandprojectpreserve full depth-first output names. Tests cover nested selection, pr…Out of Scope Changes check The changes stay within the stated scope. They update struct-name propagation, select field offsets, aggregate grouping names, column alias validation, and related automated tests. No unrelated change… Title check The title clearly summarizes the main change and uses valid Conventional Commit syntax with a breaking-change marker. Description check The description explains the root cause, the implemented changes, out-of-scope behavior, linked issue, and breaking changes. It provides the rationale required by the template.
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Review comments at @src/substrait/builders/extended_expression.py:
- Line 605: Update the alias handling around output_names to reject a multi-name
alias when its length differs from the inferred output_names length, before
replacing the output names. Preserve the existing behavior for matching
multi-name aliases and single-name aliases.
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src/substrait/builders/extended_expression.pysrc/substrait/builders/plan.pytests/builders/extended_expression/test_column.pytests/builders/plan/test_aggregate.pytests/builders/plan/test_project.py
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Now that select, project and aggregate keep every output name, an alias list on a single-valued expression leaked extra names into the plan root. Those builders now raise when an expression has more names than its output type has fields. An empty-string column() alias is again ignored rather than renaming the column to "".
…olumns # Conflicts: # tests/builders/extended_expression/test_column.py
andrew-coleman
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andrew-coleman
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The emit fix works: select(a, s) over a struct column now gives ['a', 's', 'x', 'y']. The inline comments cover two gaps in the new name check and an error message that crashes.
Breaking change. This now rejects inputs that build valid plans on main. select(t, [column("a", alias=["x", "y"])]) builds there with the name x and raises ValueError here. A multi-name alias on any non-struct expression passed to project, select or grouping does the same. column("s", alias="z") on a struct column also returns ["z", "x", "y"] instead of ["z"]. The title drives the version bump, so I think this needs fix!: and a BREAKING CHANGE: footer. Per CONTRIBUTING.md#breaking-changes, the footer goes last, below Fixes #311. Something like:
BREAKING CHANGE: `project`, `select` and `aggregate` grouping expressions now raise `ValueError` for an expression with more output names than its output type has; previously only the first name was kept. `column()` raises when an alias list has two or more names but not exactly one per field, nested fields included, and a single alias on a struct column now keeps its nested names. Rename a column with a single alias, or pass a list that names every field in depth-first order.
PR description. It ends with 🤖 Generated with AI. The description becomes the squash-merge commit body, and CONTRIBUTING.md:114 asks to keep tool-attribution lines out of it. This matters more once there's a footer: anything after BREAKING CHANGE: is absorbed into the published release note.
| if len(names) <= 1: | ||
| return names |
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On main, an expression with no output names raised IndexError here. Now it adds no names, so the plan comes out with fewer names than fields and no error. For example, select(agg, [column(2)]) on an aggregate with grouping_sets=[[0], [1]] builds root.names == [] for 1 field, because the grouping-set column has no name. A pre-built ExtendedExpression with empty output_names does the same in project, select and grouping. Failing here keeps the old fail-fast, now with a clear message:
| if len(names) <= 1: | |
| return names | |
| if not names: | |
| raise ValueError("Expression has no output names; give it an alias.") | |
| if len(names) == 1: | |
| # Struct-valued expressions other than column() still emit one name (#312). | |
| return names |
| if len(names) > needed: | ||
| raise ValueError( | ||
| f"Expression named {names!r} has {len(names)} names, but its output " | ||
| f"type has only {needed}." | ||
| ) |
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This check only rejects too many names, so a partial list gets through. select(t, [cast(column("s"), struct([i64(), i64()]), alias=["c", "p"]), column("a")]) builds ["c", "p", "a"] for 2 fields, when 4 names are needed. Column a then loses its name, and a later column("a") raises column 'a' not found; available columns: ['c']. Requiring the exact count closes this gap. The docstring on line 397 would need updating too, e.g. "checked against its output type".
| if len(names) > needed: | |
| raise ValueError( | |
| f"Expression named {names!r} has {len(names)} names, but its output " | |
| f"type has only {needed}." | |
| ) | |
| if len(names) != needed: | |
| raise ValueError( | |
| f"Expression named {names!r} has {len(names)} names, but its output " | |
| f"type needs {needed}." | |
| ) |
| if len(alias) != len(output_names): | ||
| raise ValueError( | ||
| f"column() alias {alias!r} has {len(alias)} names, but field " | ||
| f"{output_names[0]!r} needs {len(output_names)} " |
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The error message reads output_names[0], but the list can be empty. Then the message itself raises IndexError, and the intended error never appears. column(2, alias=["g", "h"]) against the grouping-set aggregate above hits this. So does any schema with too few names, such as the output of a struct-valued expression that emits one name (#312). Using field avoids it:
| f"{output_names[0]!r} needs {len(output_names)} " | |
| f"{field!r} needs {len(output_names)} " |
A partial alias list on a struct-valued expression shifted every later column's name onto the wrong field, and an expression with no output names silently added none. Both now raise ValueError, and column()'s alias-length error no longer crashes on a field that has no names.
nielspardon
changed the title
2 participants
selectcomputed its emit offset from the input's name count instead of its top-level field count. Because a struct column has one field but several depth-first names, the output mapping pointed past the end of the projected fields over any struct-typed input, andinfer_plan_schemaraisedIndexError.select,projectandaggregate(grouping expressions) also kept onlyoutput_names[0]of each expression, dropping a struct column's nested names. They now keep the full depth-firstoutput_nameslist and check it against the expression's output type.Struct-valued expressions other than
column()(functions, casts, literals,if_then, aggregate measures) still emit a single name by default. That needs a naming scheme the spec doesn't define, so it's tracked separately in #312.Fixes #311
BREAKING CHANGE:
project,selectandaggregategrouping expressions now raiseValueErrorfor an expression with two or more output names that do not match its output type, nested fields included, and for an expression with no output names; previously only the first name was kept.column()raises when an alias list has two or more names but not exactly one per field, and a single alias on a struct column now keeps its nested names (column("s", alias="z")gives["z", "x", "y"]instead of["z"]). Rename a column with a single alias, or pass a list that names every field in depth-first order.