from django.contrib.gis.gdal import CoordTransform, SpatialReference from django.core.serializers.base import SerializerDoesNotExist from django.core.serializers.json import Serializer as JSONSerializer class Serializer(JSONSerializer): """ Convert a queryset to GeoJSON, http://geojson.org/ """ def _init_options(self): super()._init_options() self.geometry_field = self.json_kwargs.pop('geometry_field', None) self.srid = self.json_kwargs.pop('srid', 4326) if (self.selected_fields is not None and self.geometry_field is not None and self.geometry_field not in self.selected_fields): self.selected_fields = list(self.selected_fields) + [self.geometry_field] def start_serialization(self): self._init_options() self._cts = {} # cache of CoordTransform's self.stream.write( '{"type": "FeatureCollection", "crs": {"type": "name", "properties": {"name": "EPSG:%d"}},' ' "features": [' % self.srid) def end_serialization(self): self.stream.write(']}') def start_object(self, obj): super().start_object(obj) self._geometry = None if self.geometry_field is None: # Find the first declared geometry field for field in obj._meta.fields: if hasattr(field, 'geom_type'): self.geometry_field = field.name break def get_dump_object(self, obj): data = { "type": "Feature", "properties": self._current, } if ((self.selected_fields is None or 'pk' in self.selected_fields) and 'pk' not in data["properties"]): data["properties"]["pk"] = obj._meta.pk.value_to_string(obj) if self._geometry: if self._geometry.srid != self.srid: # If needed, transform the geometry in the srid of the global geojson srid if self._geometry.srid not in self._cts: srs = SpatialReference(self.srid) self._cts[self._geometry.srid] = CoordTransform(self._geometry.srs, srs) self._geometry.transform(self._cts[self._geometry.srid]) data["geometry"] = eval(self._geometry.geojson) else: data["geometry"] = None return data def handle_field(self, obj, field): if field.name == self.geometry_field: self._geometry = field.value_from_object(obj) else: super().handle_field(obj, field) class Deserializer: def __init__(self, *args, **kwargs): raise SerializerDoesNotExist("geojson is a serialization-only serializer")