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from __future__ import unicode_literals
from django.contrib.gis.gdal import HAS_GDAL
from django.core.serializers.base import (
SerializationError, SerializerDoesNotExist,
)
from django.core.serializers.json import Serializer as JSONSerializer
if HAS_GDAL:
from django.contrib.gis.gdal import CoordTransform, SpatialReference
class Serializer(JSONSerializer):
"""
Convert a queryset to GeoJSON, http://geojson.org/
"""
def _init_options(self):
super(Serializer, self)._init_options()
self.geometry_field = self.json_kwargs.pop('geometry_field', None)
self.srs = SpatialReference(self.json_kwargs.pop('srid', 4326))
def start_serialization(self):
if not HAS_GDAL:
# GDAL is needed for the geometry.geojson call
raise SerializationError("The geojson serializer requires the GDAL library.")
self._init_options()
self._cts = {} # cache of CoordTransform's
self.stream.write(
'{"type": "FeatureCollection", "crs": {"type": "name", "properties": {"name": "EPSG:%d"}},'
' "features": [' % self.srs.srid)
def end_serialization(self):
self.stream.write(']}')
def start_object(self, obj):
super(Serializer, self).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._geometry:
if self._geometry.srid != self.srs.srid:
# If needed, transform the geometry in the srid of the global geojson srid
if self._geometry.srid not in self._cts:
self._cts[self._geometry.srid] = CoordTransform(self._geometry.srs, self.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._get_val_from_obj(obj)
else:
super(Serializer, self).handle_field(obj, field)
class Deserializer(object):
def __init__(self, *args, **kwargs):
raise SerializerDoesNotExist("geojson is a serialization-only serializer")
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