Get random point from django PolygonField

Question

TL,DR; I want to get a random point from a polygon (potentially) using ST_GeneratePoints.

---

Background

I'm making a GeoDjango web service and have a collection of UK Postcodes with respective boundaries like so:

from django.db import models as dj_models
from django.contrib.gis.db import models as gis_models

class Postcode(gis_models.Model):
      pretty_postcode = dj_models.CharField( max_length=8 )
      coords = gis_models.PolygonField( default='POLYGON EMPTY' )

I've found a delightful little PostGIS function ST_GeneratePoints, which can find me random points in my coords region.

Question

How can I use this function from within my python django app (or can you suggest a better way?). Ideally ending up with a function like so:

from django.contrib.gis import geos
# ... other imports ...

class Postcode(gis_models.Model):
     # ... fields ...

     def get_random_point(self):
         rand_point = # code that executes ST_GeneratePoints
                      # and returns a geos.Point instance
         return rand_point

Answer 1

I have answered a similar question here: Equivalent of PostGIS ST_MakeValid in Django GEOS

Since you essentially want to call a database function, you cannot quite do it as you imagine.
What you can do instead is to wrap the ST_GeneratePoints as a GeoFunc:

from django.contrib.gis.db.models.functions import GeoFunc

class GeneratePoints(GeoFunc):
    function='ST_GeneratePoints'

and use it in an aggregation/annotation:

from django.db.models import Value

Postcode.objects.annotate(
    rand_point=GeneratePoints(
        'coords',
        Value(1) # to get only one point
    )
)

Another way of doing the same thing is:

from django.contrib.gis.db.models.functions import GeoFunc
from django.db.models import F, Value

Postcode.objects.annotate(
    rand_point=GeoFunc(
        F('coords'),
        Value(1),
        function='ST_GeneratePoints',
    )
)