[Solved] MakeValid not working for a single model object

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As stated in the linked post MakeValid is a database function, which means that it can be executed only during querying the database.

It is 1-to-1 similar to the PostGIS usage of ST_MakeValid which cannot be executed outside of a table query (cannot exist autonomously).

When you create the np object, and then you try to do:

np.polygon = MakeValid(np.polygon)

You are essentially trying to apply a database function to an instance of the ‘MyModel’ class which isn’t supposed to work! (as it does not)

What you can do:

  1. You can create a query to update a specific table row:

    np = MyModel.objects.filter(id=np.id).update(polygon=MakeValid('polygon'))

    Note: The object with id=np.id‘s polygon, will be updated in the
    database permanently with that method.

  2. You can utilize the GEOSGeometry.buffer():

    Using polygon.buffer(0) can tidy up most of the polygon irregularities (it can even solve some types of “bowtie”/self-intersecting polygons)

    np.polygon.valid          # False
np.polygon.buffer(0)      # Make valid with buffer(0)
np.polygon.valid          # True

  3. Finally, you can use Shapely and create a shapely polygon for your calculations which you can make valid with the same method as above (both Shapely’s buffer and GeoDjango’s buffer use GEOS library):

    from shapely.geometry import Polygon

# Initialize the polygon object with one of the following ways:
np_polygon = Polygon([np.polygon.coords])
# or
np_polygon = Polygon(np.polygon.wkt)

np_polygon.is_valid                 # False
np_polygon = np_polygon.buffer(0)   # Make valid with buffer(0)
np_polygon.is_valid                 # True

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solved MakeValid not working for a single model object