Geodjango Query: All Point That Are Contained Into A Multi Polygon

I have two models: Model_A that contains a GeoDjango Point; Model_B that contains a GeoDjnago MultiPololygon; For every element in Model_A I have to check if the point is contain

Solution 1:

From Django version 1.11 you have an optimized option to solve this query.

Assumptions:

1. Model_A has a geometry field called: model_a_point.
2. Model_B has a geometry field called: model_b_poly.

Methods used:

1. Subquery(), new method in Django 1.11 which allows the definition of queries with a subquery part.

2. OuterRef(), new method in Django 1.11 which is used:

   when a queryset in a Subquery needs to refer to a field from the outer query.

3. within(), which:

   Tests if the geometry field is spatially within the lookup geometry.

4. annotate(), which will generate for each item in a queryset, a new field (in our case it will contain the points contained by a polygon.)

Query:

Model_B.objects.annotate(
    contained_points=Subquery(
        Model_A.objects.filter(
            model_a_point__within=OuterRef('model_b_poly')
        )  # Ref: 1, referenced below, keep reading
    )
)

Result and something more:

The query above will have a field contained_points for every polygon in Model_B which contains every point from Model_A contained by this polygon.

If you only want to keep geometry field of those points (lon, lan), at the end of the Subquery call (Ref: 1), use the values() method.