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