| """ |
| 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 |
