redis/redis-py · error · ValueError

collect sort_by must contain at least one field

Error message

collect sort_by must contain at least one field

What it means

Raised by the collect reducer constructor when sort_by is provided but resolves to zero sort fields (e.g. an empty list). COLLECT's SORTBY clause needs at least one Asc/Desc field; an empty sort list is a caller bug.

Solutions

1. Omit sort_by entirely if no ordering is needed.
2. Pass at least one Asc or Desc instance: collect(sort_by=Desc('price')).
3. Guard dynamic lists: only set sort_by when it is non-empty.

Example fix

// before
r = collect(fields='*', sort_by=sort_list)  # sort_list == []
// after
from redis.commands.search.aggregation import Desc
r = collect(fields='*', sort_by=sort_list or Desc('price'))
# or omit it
r = collect(fields='*')

sort_by = sort_by if (isinstance(sort_by, (Asc, Desc)) or (sort_by and len(list(sort_by)) > 0)) else None
collect(fields=fields, sort_by=sort_by)

try:
    r = collect(fields=fields, sort_by=sort_by)
except ValueError:
    r = collect(fields=fields)

When it happens

Trigger: Calling collect(sort_by=[]) or collect(sort_by=iter([])). Passing a filtered list that became empty.

Common situations: Building sort_by dynamically from user input that produced no fields. Mixing up Asc/Desc instances with raw strings so the list is structurally empty after processing.

Related errors

• collect fields must be '*' or a non-empty list of names
• Cannot use FIELDNAME alias with no field
• Did not receive a SortByField.
• AGGREGATION requires exactly one aggregation spec per key
• At least one tag must be specified

AI-assisted analysis of redis/redis-py@6a6b581b48 (2026-08-10). Data as JSON: /api/errors/e177c6e184b3d5ca. Report an issue: GitHub.

Appendix: source

Thrown at redis/commands/search/reducers.py:253

            if not names or any(not n.strip() for n in names):
                raise ValueError(
                    "collect fields must be '*' or a non-empty list of names"
                )
            names = [_ensure_at_prefix(n) for n in names]
            args += ["FIELDS", str(len(names))] + names

        # DISTINCT (optional)
        if distinct:
            args += ["DISTINCT"]

        # SORTBY (optional)
        if sort_by is not None:
            sort_fields = [sort_by] if isinstance(sort_by, (Asc, Desc)) else sort_by
            sort_args: list[str] = []
            for f in sort_fields:
                sort_args += [_ensure_at_prefix(f.field), f.DIRSTRING]
            if not sort_args:
                raise ValueError("collect sort_by must contain at least one field")
            args += ["SORTBY", str(len(sort_args))] + sort_args

        # LIMIT (optional)
        if limit is not None:
            offset, count = limit
            args += ["LIMIT", str(offset), str(count)]

        super().__init__(*args)

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