Correct json format to save into geoalchemy2 Geometry field

Question

I have a json of this format:

{

     "type":"Feature",
     "properties":{},
     "geometry":{
          "type":"Point",
          "coordinates":[6.74285888671875,-3.6778915094650726]
     }
}

And a flask-geoalchemy2 defined field like this:-

from app import db
from app.mixins import TimestampMixin
from geoalchemy2 import Geometry

class Event(db.Model, TimestampMixin):
    __tablename__ = 'events'

    id = db.Column(db.BigInteger, primary_key=True)
    title = db.Column(db.Unicode(255))
    start = db.Column(db.DateTime(timezone=True))
    location = db.Column(Geometry(geometry_type='POINT', srid=4326))
    is_active = db.Column(db.Boolean(), default=False)

    def __repr__(self):
        return '<Event %r %r>' % (self.id, self.title)

Attempting to save an event object with the event.location assigned with the above json value fails with this error

DataError: (DataError) Geometry SRID (0) does not match column SRID (4326)

What's the correct format event.location has to be in order for the

db.session.add(event)
db.session.commit() 

to work correctly?

Answer 1

It was an error in the way I process my geojson. I need to explicitly state the srid that the geojson has to conform to.

This is the solution:-

def process_formdata(self, valuelist):
    """ Convert GeoJSON to DB object """
    if valuelist:
        geo_ob = geojson.loads(valuelist[0])
        # Convert the Feature into a Shapely geometry and then to GeoAlchemy2 object
        # We could do something with the properties of the Feature here...
        self.data = from_shape(asShape(geo_ob.geometry), srid=4326)
    else:
        self.data = None

Answer 2

I ended up using the following snippet: a column type that works with GeoJSON values when loading/saving data:

class GeometryJSON(Geometry):
    """ Geometry, as JSON

    The original Geometry class uses strings and transforms them using PostGIS functions:
        ST_GeomFromEWKT('SRID=4269;POINT(-71.064544 42.28787)');

    This class replaces the function with nice GeoJSON objects:
        {"type": "Point", "coordinates": [1, 1]}
    """
    from_text = 'ST_GeomFromGeoJSON'
    as_binary = 'ST_AsGeoJSON'
    ElementType = dict

    def result_processor(self, dialect, coltype):
        # Postgres will give us JSON, thanks to `ST_AsGeoJSON()`. We just return it.
        def process(value):
            return value
        return process

    def bind_expression(self, bindvalue):
        return func.ST_SetSRID(super().bind_expression(bindvalue), self.srid)

    def bind_processor(self, dialect):
        # Dump incoming values as JSON
        def process(bindvalue):
            if bindvalue is None:
                return None
            else:
                return json.dumps(bindvalue)
        return process

    @property
    def python_type(self):
        return dict