"""
The GeometryProxy object, allows for lazy-geometries. The proxy uses
Python descriptors for instantiating and setting Geometry objects
corresponding to geographic model fields.
Thanks to Robert Coup for providing this functionality (see #4322).
"""
class GeometryProxy(object):
def __init__(self, klass, field):
"""
Proxy initializes on the given Geometry class (not an instance) and
the GeometryField.
"""
self._field = field
self._klass = klass
def __get__(self, obj, type=None):
"""
This accessor retrieves the geometry, initializing it using the geometry
class specified during initialization and the HEXEWKB value of the field.
Currently, only GEOS or OGR geometries are supported.
"""
if obj is None:
# Accessed on a class, not an instance
return self
# Getting the value of the field.
geom_value = obj.__dict__[self._field.attname]
if isinstance(geom_value, self._klass):
geom = geom_value
elif (geom_value is None) or (geom_value==''):
geom = None
else:
# Otherwise, a Geometry object is built using the field's contents,
# and the model's corresponding attribute is set.
geom = self._klass(geom_value)
setattr(obj, self._field.attname, geom)
return geom
def __set__(self, obj, value):
"""
This accessor sets the proxied geometry with the geometry class
specified during initialization. Values of None, HEXEWKB, or WKT may
be used to set the geometry as well.
"""
# The OGC Geometry type of the field.
gtype = self._field.geom_type
# The geometry type must match that of the field -- unless the
# general GeometryField is used.
if isinstance(value, self._klass) and (str(value.geom_type).upper() == gtype or gtype == 'GEOMETRY'):
# Assigning the SRID to the geometry.
if value.srid is None: value.srid = self._field.srid
elif value is None or isinstance(value, (basestring, buffer)):
# Set with None, WKT, HEX, or WKB
pass
else:
raise TypeError('cannot set %s GeometryProxy with value of type: %s' % (obj.__class__.__name__, type(value)))
# Setting the objects dictionary with the value, and returning.
obj.__dict__[self._field.attname] = value
return value
|