python/lib/django_1_4/django/contrib/gis/db/models/proxy.py

   1 """
   2 The GeometryProxy object, allows for lazy-geometries.  The proxy uses
   3 Python descriptors for instantiating and setting Geometry objects
   4 corresponding to geographic model fields.
   5
   6 Thanks to Robert Coup for providing this functionality (see #4322).
   7 """
   8
   9 class GeometryProxy(object):
  10     def __init__(self, klass, field):
  11         """
  12         Proxy initializes on the given Geometry class (not an instance) and
  13         the GeometryField.
  14         """
  15         self._field = field
  16         self._klass = klass
  17
  18     def __get__(self, obj, type=None):
  19         """
  20         This accessor retrieves the geometry, initializing it using the geometry
  21         class specified during initialization and the HEXEWKB value of the field.
  22         Currently, only GEOS or OGR geometries are supported.
  23         """
  24         if obj is None:
  25             # Accessed on a class, not an instance
  26             return self
  27
  28         # Getting the value of the field.
  29         geom_value = obj.__dict__[self._field.attname]
  30
  31         if isinstance(geom_value, self._klass):
  32             geom = geom_value
  33         elif (geom_value is None) or (geom_value==''):
  34             geom = None
  35         else:
  36             # Otherwise, a Geometry object is built using the field's contents,
  37             # and the model's corresponding attribute is set.
  38             geom = self._klass(geom_value)
  39             setattr(obj, self._field.attname, geom)
  40         return geom
  41
  42     def __set__(self, obj, value):
  43         """
  44         This accessor sets the proxied geometry with the geometry class
  45         specified during initialization.  Values of None, HEXEWKB, or WKT may
  46         be used to set the geometry as well.
  47         """
  48         # The OGC Geometry type of the field.
  49         gtype = self._field.geom_type
  50
  51         # The geometry type must match that of the field -- unless the
  52         # general GeometryField is used.
  53         if isinstance(value, self._klass) and (str(value.geom_type).upper() == gtype or gtype == 'GEOMETRY'):
  54             # Assigning the SRID to the geometry.
  55             if value.srid is None: value.srid = self._field.srid
  56         elif value is None or isinstance(value, (basestring, buffer)):
  57             # Set with None, WKT, HEX, or WKB
  58             pass
  59         else:
  60             raise TypeError('cannot set %s GeometryProxy with value of type: %s' % (obj.__class__.__name__, type(value)))
  61
  62         # Setting the objects dictionary with the value, and returning.
  63         obj.__dict__[self._field.attname] = value
  64         return value