Django Queryset capabilites example

letting_agent.py

"""
This snippet will return all the letting agents, bucketed into discrete bands based on distance from
an origin point (for example, the user's current location), then sorted alphabetically within each
band. The goal being to prioritise agents in close proximity, but not excessively so -- all agents
within the same band should be given equal distance-related priority.

If there's a search term, we then boost the distance score based on the name's similiarity to the
search query.
"""
qs = LettingAgentLocation.objects.select_related("agent").filter(postcode__isnull=False)

ordering = ("location_name", "-id")

if origin:
    qs = qs.annotate(
        distance=Distance("location", origin),
        distance_score=Case(
            When(location__isnull=True, then=Value(1)),
            When(distance__lte=D(km=2), then=Value(5)),
            When(distance__lte=D(km=5), then=Value(4)),
            When(distance__lte=D(km=10), then=Value(3)),
            When(distance__lte=D(km=20), then=Value(2)),
            default=Value(1),
        ),
    )
    ordering = ("-distance_score",) + ordering
if len(search_term) >= 3:
    qs = qs.annotate(
        similarity=Cast(
            TrigramWordSimilarity("location_name", search_term),
            output_field=FloatField(),
        ),
        score=(1 + Ln(F("distance_score"))) * F("similarity"),
    ).filter(
        similarity__gt=0.2,
    )
    ordering = ("-score",) + ordering
else:
    qs = qs.filter(distance_score__gte=2)