ADR 0003 — A range filter takes in the whole of its last period#

Status: accepted

Decision#

PartialDateRangeFilter finds a row when it sorts at or after the first bound and at or before the last day of the period of the second bound. 1991-03 as the second bound compares as 1991-03-31, and 1991 as 1991-12-31.

A range filter therefore finds nothing only when its first bound sorts after that last day. 1991-03-15 to 1991-03 finds the rest of March, and 1991-04 to 1991-03 finds nothing.

The range lookup on the model field does not change. Its second bound is a position in the sort order, so collected__range=("1991-03-15", "1991-03") finds nothing. These are the two public things in this package called range, and they answer differently on purpose. A filter declared with PartialDateFilter(lookup_expr="lte") is the plain lookup and keeps its position.

Why#

A lookup is written by a developer who can read its rules. A range filter is filled in by a person on a page, who takes “to March 1991” to include the middle of March. With the lookup’s rule, 1991-03-15 would be dropped from that list. That is a wrong answer and not an uncertain one, because the date is certainly inside what the person asked for.

Option	Result
Follow the lookup exactly	Rejected. Every project would either show the wrong list or write the same correction, and saving that is what the filter is for.
Change the lookup to match	Rejected. A bound as a position is what makes `gte`, `lte`, `range` and `order_by` one rule that an index serves, and FS-003 documents it filter by filter.
Widen the second bound in the filter	Chosen. It uses the `end` the value already gives, and the result is still one comparison on the column.

The lower bound needs no change. Every date in 1990-06 already sorts at or after it.

Uncertain matches stay where the sort order puts them, as they do for every lookup: 1990 is outside a range from 1990-06, and 1991 is inside a range to 1991-03. A rule that included or left out every uncertain date would be a second rule, and django-filter’s method is there for a developer who needs one.

Revisit if#

Projects keep declaring the lookup’s position for their range filters, which would mean people on those sites read a bound as a position after all.