django1/django/contrib/gis/db/models/proxy.py

"""
The SpatialProxy object allows for lazy-geometries and lazy-rasters. The proxy
uses Python descriptors for instantiating and setting Geometry or Raster
objects corresponding to geographic model fields.

Thanks to Robert Coup for providing this functionality (see #4322).
"""
from django.utils import six


class SpatialProxy(object):
    def __init__(self, klass, field):
        """
        Proxy initializes on the given Geometry or Raster class (not an instance)
        and the corresponding field.
        """
        self._field = field
        self._klass = klass

    def __get__(self, obj, type=None):
        """
        This accessor retrieves the geometry or raster, initializing it using
        the corresponding class specified during initialization and the value
        of the field. Currently, GEOS or OGR geometries as well as GDALRasters
        are supported.
        """
        if obj is None:
            # Accessed on a class, not an instance
            return self

        # Getting the value of the field.
        geo_value = obj.__dict__[self._field.attname]

        if isinstance(geo_value, self._klass):
            geo_obj = geo_value
        elif (geo_value is None) or (geo_value == ''):
            geo_obj = None
        else:
            # Otherwise, a geometry or raster object is built using the field's
            # contents, and the model's corresponding attribute is set.
            geo_obj = self._klass(geo_value)
            setattr(obj, self._field.attname, geo_obj)
        return geo_obj

    def __set__(self, obj, value):
        """
        This accessor sets the proxied geometry or raster with the
        corresponding class specified during initialization.

        To set geometries, values of None, HEXEWKB, or WKT may be used.
        To set rasters, JSON or dict values may be used.
        """
        # The geographic type of the field.
        gtype = self._field.geom_type

        if gtype == 'RASTER' and (value is None or isinstance(value, six.string_types + (dict, self._klass))):
            # For raster fields, assure input is None or a string, dict, or
            # raster instance.
            pass
        elif isinstance(value, self._klass) and (str(value.geom_type).upper() == gtype or gtype == 'GEOMETRY'):
            # The geometry type must match that of the field -- unless the
            # general GeometryField is used.
            if value.srid is None:
                # Assigning the field SRID if the geometry has no SRID.
                value.srid = self._field.srid
        elif value is None or isinstance(value, six.string_types + (six.memoryview,)):
            # Set geometries with None, WKT, HEX, or WKB
            pass
        else:
            raise TypeError('Cannot set %s SpatialProxy (%s) with value of type: %s' % (
                obj.__class__.__name__, gtype, type(value)))

        # Setting the objects dictionary with the value, and returning.
        obj.__dict__[self._field.attname] = value
        return value