id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
33344	Define bounds transform for discrete postgres range fields	Vidir Valberg Gudmundsson		"The fix for https://code.djangoproject.com/ticket/27147 adressed the issue of non-discrete range types. Left is the issue of how the ranges are ""represented"" when brought back from the database.

At $WORK we have a model like so:

{{{
class Foo(models.Model):
    ...
    period = models.DateRangeField()
}}}



The problem arises when we display the periods of multiple `Foo`s. Using the default bound of `[)` returned by postgres means that adjacent `Foo`s ""visually"" share a date in the upper of one and lower of the other. We could of course handle this ''each time'' we output the value by decrementing the upper value. But this is a bit error prone and can lead to confusions.

I propose that we add something along the lines of the following to `django.contrib.postres.fields.ranges` (heavily inspired by Jakub Skałeckis comment at https://code.djangoproject.com/ticket/27147#comment:8):

{{{
class DiscreteRangeField(RangeField):

    def __init__(self, *args, bounds_transform=CANONICAL_RANGE_BOUNDS, **kwargs):
        if bounds_transform not in ALLOWED_BOUNDS:
            raise ValueError(""bounds_transform must be one of '[)', '(]', '()', or '[]'."")
        self.bounds_transform = bounds_transform
        super().__init__(*args, **kwargs)

    def from_db_value(self, value, expression, connection):
        if value is None:
            return

        if self.bounds_transform[0] == ""("" and value.lower:
            value._lower = value.lower - self.bounds_transform_unit

        if self.bounds_transform[1] == ""]"" and value.upper:
            value._lower = value.upper - self.bounds_transform_unit

        value._bounds = self.bounds_transform
        return value
}}}

and make `IntegerRangeField`, `BigIntegerRangeField` and `DateRangeField` inherit from `DiscreteRangeField`.

I have already written some tests, and if there are no big gotchas to this approach I would love to submit a PR in the next couple of days."	New feature	closed	contrib.postgres	dev	Normal	needsinfo			Unreviewed	0	0	0	0	0	0