Opened 3 weeks ago

Closed 3 weeks ago

#36845 closed New feature (needsnewfeatureprocess)

Allow negative index in Left() for PostgreSQL

Reported by: Christopher Covington Owned by: Moksha Choksi
Component: Database layer (models, ORM) Version: 6.0
Severity: Normal Keywords:
Cc: Christopher Covington Triage Stage: Unreviewed
Has patch: no Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no

Description

PostgreSQL has supported negative indices since v9.1 ​https://www.postgresql.org/docs/9.1/functions-string.html as right side trim length--just like Python string slicing.

Targeting the check and ValueError in Left.__init__() more precisely will enable straightforward translation of a common string manipulation pattern from Python:
field[:-3]

to Django ORM for PostgreSQL:
Left('field', -3)

For other databases I would propose initially carrying forward the non-negative requirement. If there's interest, a Python implementation of negative index (right side trim length) support, or something cleverer, could follow up as separate discussion and work.

Change History (3)

comment:1 by Moksha Choksi, 3 weeks ago

Owner: set to Moksha Choksi
Status: new → assigned

comment:2 by Moksha Choksi, 3 weeks ago

Has patch: set

comment:3 by Jacob Walls, 3 weeks ago

Easy pickings: unset
Has patch: unset
Resolution: → needsnewfeatureprocess
Status: assigned → closed

Hi, thanks for the idea. It would help to know what advantage this would provide over using Right(). The best place to have this discussion would be on the new features board at django/new-features.

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