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80 lines
3.0 KiB
Python
80 lines
3.0 KiB
Python
5 years ago
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"""
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The SpatialProxy object allows for lazy-geometries and lazy-rasters. The proxy
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uses Python descriptors for instantiating and setting Geometry or Raster
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objects 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.db.models.query_utils import DeferredAttribute
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class SpatialProxy(DeferredAttribute):
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def __init__(self, klass, field, load_func=None):
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"""
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Initialize on the given Geometry or Raster class (not an instance)
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and the corresponding field.
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"""
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self._klass = klass
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self._load_func = load_func or klass
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super().__init__(field)
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def __get__(self, instance, cls=None):
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"""
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Retrieve the geometry or raster, initializing it using the
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corresponding class specified during initialization and the value of
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the field. Currently, GEOS or OGR geometries as well as GDALRasters are
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supported.
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"""
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if instance 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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try:
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geo_value = instance.__dict__[self.field.attname]
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except KeyError:
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geo_value = super().__get__(instance, cls)
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if isinstance(geo_value, self._klass):
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geo_obj = geo_value
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elif (geo_value is None) or (geo_value == ''):
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geo_obj = None
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else:
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# Otherwise, a geometry or raster object is built using the field's
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# contents, and the model's corresponding attribute is set.
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geo_obj = self._load_func(geo_value)
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setattr(instance, self.field.attname, geo_obj)
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return geo_obj
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def __set__(self, instance, value):
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"""
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Retrieve the proxied geometry or raster with the corresponding class
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specified during initialization.
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To set geometries, use values of None, HEXEWKB, or WKT.
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To set rasters, use JSON or dict values.
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"""
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# The geographic type of the field.
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gtype = self.field.geom_type
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if gtype == 'RASTER' and (value is None or isinstance(value, (str, dict, self._klass))):
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# For raster fields, assure input is None or a string, dict, or
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# raster instance.
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pass
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elif isinstance(value, self._klass):
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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 value.srid is None:
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# Assigning the field SRID if the geometry has no SRID.
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value.srid = self.field.srid
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elif value is None or isinstance(value, (str, memoryview)):
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# Set geometries 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 SpatialProxy (%s) with value of type: %s' % (
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instance.__class__.__name__, gtype, type(value)))
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# Setting the objects dictionary with the value, and returning.
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instance.__dict__[self.field.attname] = value
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return value
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