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