PostgreSQL specific Django Percentile aggregation function

Readme.md

Inspired by this gist

The class extends to calculate any percentile (not just median).

Example usage:

Percentile('some_field', percentile=0.5) # calculates median for the field
Percentile('some_field', percentile=0.9) # calculates the 90th percentile

For completeness, I can calculate the median age of some Student model like so:

Student.objects.aggregate(median_age=Percentile('age', percentile=0.5))

It also works when used in annotate query.

More info at the official django documentation site

percentile.py

from django.db.modesl import Aggregate, FloatField

class Percentile(Aggregate):
    function = "PERCENTILE_CONT"
    name = "median"
    output_field = FloatField()
    template = "%(function)s (%(percentile)s) WITHIN GROUP (ORDER BY %(expressions)s)"