CODEWITHSUNDEEP
pythondjangodjango-ormgeodjango
Safari
Safari

Reputation: 11935

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 contained into some m_polygon of Model_B element;

I'm able to make this simple query.

But I also thought: I have a lot of elements in Model_A and few elements in Model_B. So, probably is more efficient to iterate all elements in Model_B and check if exist some element in Model_A that it is contained into the current Model_B element.

So, is there any way to make this GeoDjango query?

Something like this:

Model_A.objects.filter(*point_is_contained_into*=a_model_b_mpolygon);

------------------ EDIT -----------------

I tried to use this:

result = Model_A.objects.filter(position__intersects=a_model_b_mpolygon)

And this works for me. Are there contraindications to use this type of query in my case?

Upvotes: 4

Views: 1988

Answers (1)

John Moutafis
John Moutafis

Reputation: 23134

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.

Upvotes: 3

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